diff --git a/diylc/diylc-core/src/main/java/org/diylc/common/BuildingBlock.java b/diylc/diylc-core/src/main/java/org/diylc/common/BuildingBlock.java
index b7dd1653..94a707b6 100644
--- a/diylc/diylc-core/src/main/java/org/diylc/common/BuildingBlock.java
+++ b/diylc/diylc-core/src/main/java/org/diylc/common/BuildingBlock.java
@@ -21,6 +21,7 @@
 */
 package org.diylc.common;
 
+import java.time.LocalDateTime;
 import java.util.Collection;
 
 import org.diylc.core.IDIYComponent;
@@ -29,6 +30,10 @@ public class BuildingBlock {
 
   private String name;
   private Collection<IDIYComponent<?>> components;
+  // the dates are set only on factory blocks in import-defaults/blocks.xml, and a withdrawn
+  // factory block carries nothing but its name and deletedOn
+  private LocalDateTime createdOn;
+  private LocalDateTime deletedOn;
 
   public BuildingBlock(String name, Collection<IDIYComponent<?>> components) {
     super();
@@ -52,6 +57,22 @@ public class BuildingBlock {
     this.components = components;
   }
 
+  public LocalDateTime getCreatedOn() {
+    return createdOn;
+  }
+
+  public void setCreatedOn(LocalDateTime createdOn) {
+    this.createdOn = createdOn;
+  }
+
+  public LocalDateTime getDeletedOn() {
+    return deletedOn;
+  }
+
+  public void setDeletedOn(LocalDateTime deletedOn) {
+    this.deletedOn = deletedOn;
+  }
+
   @Override
   public String toString() {
     return name;
diff --git a/diylc/diylc-core/src/main/java/org/diylc/common/IBlockProcessor.java b/diylc/diylc-core/src/main/java/org/diylc/common/IBlockProcessor.java
index 3dcc369b..a14428d1 100644
--- a/diylc/diylc-core/src/main/java/org/diylc/common/IBlockProcessor.java
+++ b/diylc/diylc-core/src/main/java/org/diylc/common/IBlockProcessor.java
@@ -27,6 +27,7 @@ public interface IBlockProcessor {
 
   public static final String BLOCKS_KEY = "buildingBlocks";
   public static final String DEFAULT_BLOCKS_IMPORTED_KEY = "defaultBlocksImported";
+  public static final String DEFAULT_BLOCKS_IMPORT_DATE_KEY = "defaultBlocksImportDate";
 
   /**
    * Prefix that marks a string as a reference to a building block rather than a component class
diff --git a/diylc/diylc-core/src/main/java/org/diylc/presenter/BuildingBlockManager.java b/diylc/diylc-core/src/main/java/org/diylc/presenter/BuildingBlockManager.java
index 6429f55b..78edbfb8 100644
--- a/diylc/diylc-core/src/main/java/org/diylc/presenter/BuildingBlockManager.java
+++ b/diylc/diylc-core/src/main/java/org/diylc/presenter/BuildingBlockManager.java
@@ -18,6 +18,7 @@
 package org.diylc.presenter;
 
 import java.io.*;
+import java.time.LocalDateTime;
 import java.util.*;
 
 import org.apache.log4j.Logger;
@@ -28,6 +29,7 @@ import com.thoughtworks.xstream.io.xml.DomDriver;
 import com.thoughtworks.xstream.security.AnyTypePermission;
 
 import org.diylc.common.BlockInstantiationMode;
+import org.diylc.common.BuildingBlock;
 import org.diylc.common.BuildingBlockPackage;
 import org.diylc.common.ComponentType;
 import org.diylc.common.IBlockProcessor;
@@ -42,7 +44,7 @@ public class BuildingBlockManager {
 
   private static final String BLOCKS_FILE_NAME = "import-defaults/blocks.xml";
 
-  private static final Logger LOG = Logger.getLogger(VariantManager.class);
+  private static final Logger LOG = Logger.getLogger(BuildingBlockManager.class);
 
   private IConfigurationManager<?> configManager;
   private XStream xStream;
@@ -58,44 +60,80 @@ public class BuildingBlockManager {
 
   @SuppressWarnings("unchecked")
   public void importDefaultBlocks() {
-    // import default templates from variants.xml file only if we didn't do it already
-    if (!configManager.readBoolean(IPlugInPort.DEFAULT_BLOCKS_IMPORTED_KEY, false)) {
-      try {
-        InputStream inputStream = Presenter.class.getResourceAsStream("/" + BLOCKS_FILE_NAME);
-        if (inputStream == null) {
-          return;
-        }
-        BufferedInputStream in = new BufferedInputStream(inputStream);
-          Map<String, List<IDIYComponent<?>>> defaults =
-              (Map<String, List<IDIYComponent<?>>>) ProjectFileManager.xStreamSerializer
-                  .fromXML(in);
-          in.close();
-
-          Map<String, List<IDIYComponent<?>>> blocksMap =
-              (Map<String, List<IDIYComponent<?>>>) configManager.readObject(IPlugInPort.BLOCKS_KEY,
-                  null);
-          if (blocksMap == null)
-            blocksMap = new HashMap<String, List<IDIYComponent<?>>>();
-
-          // merge default blocks with user's
-          for (Map.Entry<String, List<IDIYComponent<?>>> entry : defaults.entrySet()) {
-            if (!blocksMap.containsKey(entry.getKey()))
-              blocksMap.put(entry.getKey(), entry.getValue());
-          }
-
-          // update templates and a flag marking that we imported them
-          configManager.writeValue(IPlugInPort.DEFAULT_BLOCKS_IMPORTED_KEY, true);
-          configManager.writeValue(IPlugInPort.BLOCKS_KEY, blocksMap);
-          int importCount = defaults.size();
-          if (importCount > 0) {
-            LOG.info(String.format("Imported %d default building blocks", importCount));
-          }
-      } catch (Exception e) {
-        LOG.error("Could not load default blocks", e);
+    try {
+      InputStream inputStream = Presenter.class.getResourceAsStream("/" + BLOCKS_FILE_NAME);
+      if (inputStream == null) {
+        return;
       }
+      BufferedInputStream in = new BufferedInputStream(inputStream);
+      List<BuildingBlock> defaults =
+          (List<BuildingBlock>) ProjectFileManager.xStreamSerializer.fromXML(in);
+      in.close();
+      importDefaultBlocks(defaults);
+    } catch (Exception e) {
+      LOG.error("Could not load default blocks", e);
     }
   }
-  
+
+  @SuppressWarnings("unchecked")
+  void importDefaultBlocks(List<BuildingBlock> defaults) {
+    LocalDateTime importDate = (LocalDateTime) configManager
+        .readObject(IPlugInPort.DEFAULT_BLOCKS_IMPORT_DATE_KEY, LocalDateTime.MIN);
+
+    Map<String, List<IDIYComponent<?>>> blocksMap =
+        (Map<String, List<IDIYComponent<?>>>) configManager.readObject(IPlugInPort.BLOCKS_KEY,
+            null);
+    if (blocksMap == null) {
+      blocksMap = new HashMap<String, List<IDIYComponent<?>>>();
+    }
+
+    // as with variants, the import date is the latest date in the bundled file rather than the
+    // clock, and never moves backwards
+    LocalDateTime newImportDate = importDate;
+    List<String> deletedNames = new ArrayList<String>();
+    int importCount = 0;
+
+    for (BuildingBlock block : defaults) {
+      if (block.getCreatedOn() != null && block.getCreatedOn().isAfter(newImportDate)) {
+        newImportDate = block.getCreatedOn();
+      }
+      if (block.getDeletedOn() != null && block.getDeletedOn().isAfter(newImportDate)) {
+        newImportDate = block.getDeletedOn();
+      }
+      // a deletion stub keeps nothing but its name, so a missing createdOn only means an old
+      // entry when the block has not been deleted
+      boolean created = block.getCreatedOn() == null ? block.getDeletedOn() == null
+          : importDate.compareTo(block.getCreatedOn()) < 0;
+      boolean deleted =
+          block.getDeletedOn() != null && importDate.compareTo(block.getDeletedOn()) < 0;
+      if (deleted && !created) {
+        if (blocksMap.remove(block.getName()) != null) {
+          deletedNames.add(block.getName());
+        }
+      } else if (created && block.getDeletedOn() == null
+          && !blocksMap.containsKey(block.getName())) {
+        // a user who had the block before the import date existed keeps their copy, edited or
+        // not, and one who deleted it gets it back once
+        blocksMap.put(block.getName(), new ArrayList<IDIYComponent<?>>(block.getComponents()));
+        importCount++;
+      }
+    }
+
+    // the flag stays so that older versions, which know nothing else, do not import again
+    configManager.writeValue(IPlugInPort.DEFAULT_BLOCKS_IMPORTED_KEY, true);
+    configManager.writeValue(IPlugInPort.DEFAULT_BLOCKS_IMPORT_DATE_KEY, newImportDate);
+    configManager.writeValue(IPlugInPort.BLOCKS_KEY, blocksMap);
+    for (String name : deletedNames) {
+      removeFromRecent(name);
+    }
+    if (importCount > 0) {
+      LOG.info(String.format("Imported %d default building blocks", importCount));
+    }
+    if (!deletedNames.isEmpty()) {
+      LOG.info(String.format("Deleted %d withdrawn default building blocks", deletedNames.size()));
+    }
+  }
+
   @SuppressWarnings("unchecked")
   public int importBlocks(String fileName) throws IOException {
     LOG.debug(String.format("importBlocks(%s)", fileName));
@@ -221,14 +259,15 @@ public class BuildingBlockManager {
     blocks.put(blockName, blockComponents);
 
     if (System.getProperty("org.diylc.WriteStaticBlocks", "false").equalsIgnoreCase("true")) {
-      Map<String, List<IDIYComponent<?>>> defaultBlockMap =
-          new HashMap<String, List<IDIYComponent<?>>>();
-      defaultBlockMap.put(blockName, blockComponents);
+      BuildingBlock defaultBlock = new BuildingBlock(blockName, blockComponents);
+      defaultBlock.setCreatedOn(LocalDateTime.now().withNano(0));
+      List<BuildingBlock> defaultBlocks = new ArrayList<BuildingBlock>();
+      defaultBlocks.add(defaultBlock);
       try {
         BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(BLOCKS_FILE_NAME));
         XStream xStream = new XStream(new DomDriver());
         xStream.addPermission(AnyTypePermission.ANY);
-        xStream.toXML(defaultBlockMap, out);
+        xStream.toXML(defaultBlocks, out);
         out.close();
         LOG.info("Saved default blocks");
       } catch (IOException e) {
@@ -248,11 +287,16 @@ public class BuildingBlockManager {
       blocks.remove(blockName);
       configManager.writeValue(IBlockProcessor.BLOCKS_KEY, blocks);
     }
+    removeFromRecent(blockName);
+  }
 
-    // drop the block from the recently used list too, so it doesn't linger as a dead entry
+  // drop the block from the recently used list too, so it doesn't linger as a dead entry
+  @SuppressWarnings("unchecked")
+  private void removeFromRecent(String blockName) {
     List<String> recent =
         (List<String>) configManager.readObject(IPlugInPort.RECENT_COMPONENTS_KEY, null);
-    if (recent != null && recent.remove(IBlockProcessor.BLOCK_PREFIX + blockName))
+    if (recent != null && recent.remove(IBlockProcessor.BLOCK_PREFIX + blockName)) {
       configManager.writeValue(IPlugInPort.RECENT_COMPONENTS_KEY, recent);
+    }
   }
 }
diff --git a/diylc/diylc-core/src/main/java/org/diylc/presenter/VariantManager.java b/diylc/diylc-core/src/main/java/org/diylc/presenter/VariantManager.java
index 4e8f48ab..9a534742 100644
--- a/diylc/diylc-core/src/main/java/org/diylc/presenter/VariantManager.java
+++ b/diylc/diylc-core/src/main/java/org/diylc/presenter/VariantManager.java
@@ -86,6 +86,11 @@ public class VariantManager {
       if (variantMap == null)
         variantMap = new HashMap<String, List<Template>>();
 
+      // the import date records how far the bundled file reaches, not when it was read, so that
+      // running an older build first does not mark the variants of a newer build as already seen;
+      // it never moves backwards, so running an older build after a newer one changes nothing
+      LocalDateTime newImportDate = importDate;
+
       // merge default variants with user's
       for (Map.Entry<String, List<Template>> entry : defaults.entrySet()) {
         List<Template> existingVariants = variantMap.computeIfAbsent(entry.getKey(), key -> new ArrayList<Template>());
@@ -94,6 +99,12 @@ public class VariantManager {
           .collect(Collectors.toSet());
 
         for (Template variant : entry.getValue()) {
+          if (variant.getCreatedOn() != null && variant.getCreatedOn().isAfter(newImportDate)) {
+            newImportDate = variant.getCreatedOn();
+          }
+          if (variant.getDeletedOn() != null && variant.getDeletedOn().isAfter(newImportDate)) {
+            newImportDate = variant.getDeletedOn();
+          }
           // a deletion stub keeps nothing but its name, so a missing createdOn only means an old
           // entry when the variant has not been deleted
           boolean created = variant.getCreatedOn() == null ? variant.getDeletedOn() == null
@@ -116,8 +127,7 @@ public class VariantManager {
       }
 
       // update templates and a flag marking that we imported them
-      configManager.writeValue(IPlugInPort.DEFAULT_TEMPLATES_IMPORT_DATE_KEY,
-          LocalDateTime.now());
+      configManager.writeValue(IPlugInPort.DEFAULT_TEMPLATES_IMPORT_DATE_KEY, newImportDate);
       configManager.writeValue(IPlugInPort.TEMPLATES_KEY, variantMap);
       if (importCount > 0) {
         LOG.info(String.format("Imported default %d variants", importCount));
diff --git a/diylc/diylc-core/src/main/resources/import-defaults/blocks.xml b/diylc/diylc-core/src/main/resources/import-defaults/blocks.xml
index d4d217c4..0015d002 100644
--- a/diylc/diylc-core/src/main/resources/import-defaults/blocks.xml
+++ b/diylc/diylc-core/src/main/resources/import-defaults/blocks.xml
@@ -1,7 +1,8 @@
-<map>
-    <entry>
-      <string>TO-92 w/ 3 Leads</string>
-      <list>
+<list>
+    <org.diylc.common.BuildingBlock>
+      <name>TO-92 w/ 3 Leads</name>
+      <createdOn>2026-01-01T00:00:00</createdOn>
+      <components class="list">
         <diylc.connectivity.Jumper>
           <name>J1</name>
           <alpha>127</alpha>
@@ -73,11 +74,12 @@
           <folded>false</folded>
           <pinSpacing value="0.05" unit="in"/>
         </diylc.semiconductors.TransistorTO92>
-      </list>
-    </entry>
-    <entry>
-      <string>TO-92 w/ 2 Leads</string>
-      <list>
+      </components>
+    </org.diylc.common.BuildingBlock>
+    <org.diylc.common.BuildingBlock>
+      <name>TO-92 w/ 2 Leads</name>
+      <createdOn>2026-01-01T00:00:00</createdOn>
+      <components class="list">
         <diylc.connectivity.Jumper>
           <name>J1</name>
           <alpha>127</alpha>
@@ -131,11 +133,12 @@
           <folded>false</folded>
           <pinSpacing value="0.05" unit="in"/>
         </diylc.semiconductors.TransistorTO92>
-      </list>
-    </entry>
-    <entry>
-    <string>Title Block</string>
-    <list>
+      </components>
+    </org.diylc.common.BuildingBlock>
+    <org.diylc.common.BuildingBlock>
+    <name>Title Block</name>
+    <createdOn>2026-01-01T00:00:00</createdOn>
+    <components class="list">
       <org.diylc.components.shapes.Rectangle>
         <name>RECT1</name>
         <alpha>127</alpha>
@@ -735,6 +738,6 @@
         <verticalAlignment>CENTER</verticalAlignment>
         <orientation>DEFAULT</orientation>
       </org.diylc.components.misc.Label>
-    </list>
-  </entry>
-  </map>
\ No newline at end of file
+    </components>
+  </org.diylc.common.BuildingBlock>
+  </list>
\ No newline at end of file
diff --git a/diylc/diylc-core/src/test/java/org/diylc/presenter/DefaultBlockImportTest.java b/diylc/diylc-core/src/test/java/org/diylc/presenter/DefaultBlockImportTest.java
new file mode 100644
index 00000000..8e788b5b
--- /dev/null
+++ b/diylc/diylc-core/src/test/java/org/diylc/presenter/DefaultBlockImportTest.java
@@ -0,0 +1,246 @@
+/*
+
+    DIY Layout Creator (DIYLC).
+    Copyright (c) 2009-2025 held jointly by the individual authors.
+
+    This file is part of DIYLC.
+
+    DIYLC is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    DIYLC is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with DIYLC.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+package org.diylc.presenter;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+import java.awt.geom.Point2D;
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.diylc.appframework.miscutils.IConfigListener;
+import org.diylc.appframework.miscutils.IConfigurationManager;
+import org.diylc.common.BuildingBlock;
+import org.diylc.common.IBlockProcessor;
+import org.diylc.common.IPlugInPort;
+import org.diylc.core.IDIYComponent;
+import org.diylc.testcomponents.TwoPointTestComponent;
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * Covers {@link BuildingBlockManager#importDefaultBlocks(List)}: factory blocks reach existing
+ * users by their {@code createdOn}, withdrawn ones leave by their {@code deletedOn}, and the
+ * recorded import date comes from the bundled file rather than the clock.
+ */
+public class DefaultBlockImportTest {
+
+  private static final LocalDateTime OLDER_RELEASE = LocalDateTime.of(2026, 1, 1, 0, 0);
+  private static final LocalDateTime NEWER_RELEASE = LocalDateTime.of(2026, 6, 1, 0, 0);
+
+  private MapConfigurationManager configManager;
+  private BuildingBlockManager manager;
+
+  @Before
+  public void setUp() {
+    configManager = new MapConfigurationManager();
+    manager = new BuildingBlockManager(configManager, null, null);
+  }
+
+  @Test
+  public void freshInstallImportsEveryBlock() {
+    manager.importDefaultBlocks(
+        Arrays.asList(block("Old", OLDER_RELEASE), block("New", NEWER_RELEASE)));
+
+    assertTrue(blocks().containsKey("Old"));
+    assertTrue(blocks().containsKey("New"));
+    assertEquals(NEWER_RELEASE, importDate());
+    assertTrue(configManager.readBoolean(IPlugInPort.DEFAULT_BLOCKS_IMPORTED_KEY, false));
+  }
+
+  @Test
+  public void configFromTheOneTimeImportGetsTheMissingBlocksWithoutDuplicates() {
+    List<IDIYComponent<?>> kept = components();
+    Map<String, List<IDIYComponent<?>>> userBlocks = new HashMap<String, List<IDIYComponent<?>>>();
+    userBlocks.put("Old", kept);
+    configManager.writeValue(IPlugInPort.BLOCKS_KEY, userBlocks);
+    configManager.writeValue(IPlugInPort.DEFAULT_BLOCKS_IMPORTED_KEY, true);
+
+    manager.importDefaultBlocks(
+        Arrays.asList(block("Old", OLDER_RELEASE), block("New", OLDER_RELEASE)));
+
+    assertEquals(2, blocks().size());
+    assertSame(kept, blocks().get("Old"));
+    assertTrue(blocks().containsKey("New"));
+  }
+
+  @Test
+  public void blockOfANewerReleaseArrivesAfterAnOlderReleaseRanFirst() {
+    manager.importDefaultBlocks(Arrays.asList(block("Old", OLDER_RELEASE)));
+    manager.importDefaultBlocks(
+        Arrays.asList(block("Old", OLDER_RELEASE), block("New", NEWER_RELEASE)));
+
+    assertTrue(blocks().containsKey("New"));
+    assertEquals(NEWER_RELEASE, importDate());
+  }
+
+  @Test
+  public void olderReleaseRunAfterANewerOneLeavesTheImportDate() {
+    manager.importDefaultBlocks(
+        Arrays.asList(block("Old", OLDER_RELEASE), block("New", NEWER_RELEASE)));
+    manager.importDefaultBlocks(Arrays.asList(block("Old", OLDER_RELEASE)));
+
+    assertEquals(NEWER_RELEASE, importDate());
+  }
+
+  @Test
+  public void factoryBlockDeletedByTheUserIsNotImportedAgain() {
+    manager.importDefaultBlocks(Arrays.asList(block("Old", OLDER_RELEASE)));
+    blocks().remove("Old");
+
+    manager.importDefaultBlocks(Arrays.asList(block("Old", OLDER_RELEASE)));
+
+    assertFalse(blocks().containsKey("Old"));
+  }
+
+  @Test
+  public void userBlockOfTheSameNameIsKept() {
+    List<IDIYComponent<?>> own = components();
+    Map<String, List<IDIYComponent<?>>> userBlocks = new HashMap<String, List<IDIYComponent<?>>>();
+    userBlocks.put("New", own);
+    configManager.writeValue(IPlugInPort.BLOCKS_KEY, userBlocks);
+
+    manager.importDefaultBlocks(Arrays.asList(block("New", OLDER_RELEASE)));
+
+    assertSame(own, blocks().get("New"));
+  }
+
+  @Test
+  public void withdrawnBlockIsRemovedFromTheRecentlyUsedListToo() {
+    manager.importDefaultBlocks(Arrays.asList(block("Old", OLDER_RELEASE)));
+    List<String> recent =
+        new ArrayList<String>(Arrays.asList(IBlockProcessor.BLOCK_PREFIX + "Old"));
+    configManager.writeValue(IPlugInPort.RECENT_COMPONENTS_KEY, recent);
+
+    manager.importDefaultBlocks(Arrays.asList(withdrawn("Old", NEWER_RELEASE)));
+
+    assertFalse(blocks().containsKey("Old"));
+    assertTrue(recent.isEmpty());
+    assertEquals(NEWER_RELEASE, importDate());
+  }
+
+  @Test
+  public void blockRecreatedByTheUserAfterTheWithdrawalIsKept() {
+    manager.importDefaultBlocks(Arrays.asList(withdrawn("Old", OLDER_RELEASE)));
+    blocks().put("Old", components());
+
+    manager.importDefaultBlocks(Arrays.asList(withdrawn("Old", OLDER_RELEASE)));
+
+    assertTrue(blocks().containsKey("Old"));
+  }
+
+  @Test
+  public void blockCreatedAndWithdrawnSinceTheLastImportNeverArrives() {
+    BuildingBlock shortLived = withdrawn("Short-lived", NEWER_RELEASE);
+    shortLived.setCreatedOn(OLDER_RELEASE);
+
+    manager.importDefaultBlocks(Arrays.asList(shortLived));
+
+    assertFalse(blocks().containsKey("Short-lived"));
+  }
+
+  @SuppressWarnings("unchecked")
+  private Map<String, List<IDIYComponent<?>>> blocks() {
+    return (Map<String, List<IDIYComponent<?>>>) configManager.readObject(IPlugInPort.BLOCKS_KEY,
+        null);
+  }
+
+  private LocalDateTime importDate() {
+    return (LocalDateTime) configManager.readObject(IPlugInPort.DEFAULT_BLOCKS_IMPORT_DATE_KEY,
+        null);
+  }
+
+  private static List<IDIYComponent<?>> components() {
+    return new ArrayList<IDIYComponent<?>>(Arrays.asList(
+        new TwoPointTestComponent("R1", new Point2D.Double(0, 0), new Point2D.Double(10, 0))));
+  }
+
+  private static BuildingBlock block(String name, LocalDateTime createdOn) {
+    BuildingBlock block = new BuildingBlock(name, components());
+    block.setCreatedOn(createdOn);
+    return block;
+  }
+
+  private static BuildingBlock withdrawn(String name, LocalDateTime deletedOn) {
+    BuildingBlock block = new BuildingBlock(name, null);
+    block.setDeletedOn(deletedOn);
+    return block;
+  }
+
+  private static class MapConfigurationManager implements IConfigurationManager<Object> {
+
+    private final Map<String, Object> values = new HashMap<String, Object>();
+
+    @Override
+    public void addConfigListener(String key, IConfigListener listener) {}
+
+    @Override
+    public boolean readBoolean(String key, boolean defaultValue) {
+      return (Boolean) readObject(key, defaultValue);
+    }
+
+    @Override
+    public String readString(String key, String defaultValue) {
+      return (String) readObject(key, defaultValue);
+    }
+
+    @Override
+    public int readInt(String key, int defaultValue) {
+      return (Integer) readObject(key, defaultValue);
+    }
+
+    @Override
+    public float readFloat(String key, float defaultValue) {
+      return (Float) readObject(key, defaultValue);
+    }
+
+    @Override
+    public double readDouble(String key, double defaultValue) {
+      return (Double) readObject(key, defaultValue);
+    }
+
+    @Override
+    public Object readObject(String key, Object defaultValue) {
+      return values.containsKey(key) ? values.get(key) : defaultValue;
+    }
+
+    @Override
+    public void writeValue(String key, Object value) {
+      values.put(key, value);
+    }
+
+    @Override
+    public Object getSerializer() {
+      return null;
+    }
+
+    @Override
+    public void initialize(String appName) {}
+  }
+}
diff --git a/diylc/diylc-library/src/test/java/org/diylc/components/DefaultBlocksTest.java b/diylc/diylc-library/src/test/java/org/diylc/components/DefaultBlocksTest.java
new file mode 100644
index 00000000..2a971933
--- /dev/null
+++ b/diylc/diylc-library/src/test/java/org/diylc/components/DefaultBlocksTest.java
@@ -0,0 +1,70 @@
+/*
+
+    DIY Layout Creator (DIYLC).
+    Copyright (c) 2009-2025 held jointly by the individual authors.
+
+    This file is part of DIYLC.
+
+    DIYLC is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    DIYLC is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with DIYLC.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+package org.diylc.components;
+
+import java.io.InputStream;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import org.diylc.TestConfiguration;
+import org.diylc.common.BuildingBlock;
+import org.diylc.serialization.ProjectFileManager;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+/**
+ * Checks that {@code import-defaults/blocks.xml} loads as factory blocks, each either a full block
+ * with its {@code createdOn} or a withdrawal stub carrying only its name and {@code deletedOn}.
+ */
+public class DefaultBlocksTest {
+
+  @BeforeClass
+  public static void setUp() {
+    TestConfiguration.initialize();
+  }
+
+  @SuppressWarnings("unchecked")
+  @Test
+  public void everyFactoryBlockIsCompleteOrAStub() {
+    InputStream in = DefaultBlocksTest.class.getClassLoader()
+        .getResourceAsStream("import-defaults/blocks.xml");
+    Assert.assertNotNull("blocks.xml is not on the classpath", in);
+    List<BuildingBlock> blocks =
+        (List<BuildingBlock>) ProjectFileManager.xStreamSerializer.fromXML(in);
+
+    Assert.assertFalse(blocks.isEmpty());
+    Set<String> names = new HashSet<String>();
+    for (BuildingBlock block : blocks) {
+      Assert.assertNotNull(block.getName());
+      Assert.assertTrue("duplicate " + block.getName(), names.add(block.getName()));
+      if (block.getDeletedOn() == null) {
+        Assert.assertNotNull(block.getName(), block.getCreatedOn());
+        Assert.assertNotNull(block.getName(), block.getComponents());
+        Assert.assertFalse(block.getName(), block.getComponents().isEmpty());
+      } else {
+        Assert.assertNull(block.getName(), block.getComponents());
+      }
+    }
+  }
+}
diff --git a/diylc/diylc-library/src/test/java/org/diylc/components/DeletedVariantsTest.java b/diylc/diylc-library/src/test/java/org/diylc/components/DeletedVariantsTest.java
index c20530f3..a36a6675 100644
--- a/diylc/diylc-library/src/test/java/org/diylc/components/DeletedVariantsTest.java
+++ b/diylc/diylc-library/src/test/java/org/diylc/components/DeletedVariantsTest.java
@@ -43,7 +43,7 @@ import org.junit.Test;
 /**
  * Checks that a factory variant marked {@code deletedOn} in {@code import-defaults/variants.xml} is
  * taken out of the user's configuration only when the last import predates the deletion, and is
- * never imported.
+ * never imported, and that the recorded import date comes from the file rather than the clock.
  */
 public class DeletedVariantsTest {
 
@@ -140,6 +140,39 @@ public class DeletedVariantsTest {
     Assert.assertTrue(remaining.stream().noneMatch(t -> t.getDeletedOn() != null));
   }
 
+  @Test
+  public void importDateIsTheLatestDateInTheFile() {
+    LocalDateTime latest = LocalDateTime.MIN;
+    for (List<Template> variants : loadVariants().values()) {
+      for (Template variant : variants) {
+        if (variant.getCreatedOn() != null && variant.getCreatedOn().isAfter(latest)) {
+          latest = variant.getCreatedOn();
+        }
+        if (variant.getDeletedOn() != null && variant.getDeletedOn().isAfter(latest)) {
+          latest = variant.getDeletedOn();
+        }
+      }
+    }
+    InMemoryConfigurationManager config =
+        configWith(new ArrayList<Template>(), LocalDateTime.MIN);
+
+    importInto(config);
+
+    Assert.assertEquals(latest,
+        config.readObject(IPlugInPort.DEFAULT_TEMPLATES_IMPORT_DATE_KEY, null));
+  }
+
+  @Test
+  public void importDateNeverMovesBackwards() {
+    LocalDateTime later = LocalDateTime.of(2999, 1, 1, 0, 0);
+    InMemoryConfigurationManager config = configWith(new ArrayList<Template>(), later);
+
+    importInto(config);
+
+    Assert.assertEquals(later,
+        config.readObject(IPlugInPort.DEFAULT_TEMPLATES_IMPORT_DATE_KEY, null));
+  }
+
   private static class InMemoryConfigurationManager implements IConfigurationManager<Object> {
 
     private final Map<String, Object> values = new HashMap<String, Object>();
diff --git a/diylc/docs/plans/audio-coverage-roadmap.md b/diylc/docs/plans/audio-coverage-roadmap.md
index 391908af..b8509453 100644
--- a/diylc/docs/plans/audio-coverage-roadmap.md
+++ b/diylc/docs/plans/audio-coverage-roadmap.md
@@ -223,30 +223,31 @@ for auto-sizing a component from its value. **It has no production caller** —
 
 Building blocks are named groups of components, saved from a selection and re-placed as a unit.
 `BuildingBlockManager.importDefaultBlocks()` ships a default set in
-`diylc-core/src/main/resources/import-defaults/blocks.xml`, stored as a
-`Map<String, List<IDIYComponent<?>>>` using the `diylc` package alias
-(`aliasPackage("diylc", "org.diylc.components")`), and merges it into the user's own blocks by name.
+`diylc-core/src/main/resources/import-defaults/blocks.xml`, stored as a `List<BuildingBlock>`, each
+with its `name`, `components` (`class="list"`) and `createdOn`, using the `diylc` package alias
+(`aliasPackage("diylc", "org.diylc.components")`) for the components. It is merged into the user's
+own blocks (the unchanged `Map<String, List<IDIYComponent<?>>>` under `buildingBlocks`) by name.
 
-Three ship today: `TO-92 w/ 3 Leads`, `TO-92 w/ 2 Leads`, `Title Block`.
+Three ship today, all `createdOn` 2026-01-01: `TO-92 w/ 3 Leads`, `TO-92 w/ 2 Leads`, `Title Block`.
 
 Authoring one is a UI job, not a code job: place the components, select them, *Save as Building
-Block*, then lift the entry out of the user config into `blocks.xml`. Per D7 this is the default
-route for anything composable.
+Block*, then lift the entry out of the user config into `blocks.xml`. Running with
+`-Dorg.diylc.WriteStaticBlocks=true` writes the saved block in the bundled shape, dated now. Per D7
+this is the default route for anything composable.
 
-**The blocker (fixed in §6.6).** `importDefaultBlocks()` is wrapped in a one-shot flag:
+The import runs on every start and mirrors `VariantManager.importDefaultVariants()`:
 
-```java
-if (!configManager.readBoolean(IPlugInPort.DEFAULT_BLOCKS_IMPORTED_KEY, false)) {
-```
+- A block is imported when its `createdOn` is after the `defaultBlocksImportDate` watermark
+  (`LocalDateTime.MIN` when absent) and the user has no block of that name. A same-named user block
+  is never overwritten or duplicated.
+- A withdrawn block is a stub with only `name` and `deletedOn`; it is removed from the user's blocks
+  and recently used list when `deletedOn` is after the watermark.
+- The watermark becomes the latest `createdOn`/`deletedOn` in the file, never the clock, and never
+  moves backwards, so the order in which versions are launched does not matter.
+- `defaultBlocksImported` is still written so that versions before the watermark do not import.
 
-Once `defaultBlocksImported` is true it never runs again, so **a factory block added to `blocks.xml`
-reaches new installs only** — never anyone who has already launched the app. Any plan that
-distributes composites this way needs §6.6 first.
-
-`VariantManager.importDefaultVariants()` does not have this problem, and the asymmetry is worth
-knowing: it keeps a `defaultTemplatesImportDate` watermark, re-reads `variants.xml` on every start,
-and imports any variant whose `Template.createdOn` is newer than the watermark and whose name the
-user does not already have. New factory *variants* do reach existing users today.
+Because configs from those versions have no watermark, the first start of this version offers every
+factory block once, and a user who deleted one gets it back once.
 
 ### 5.5 Tests
 
@@ -281,8 +282,7 @@ block for the unreleased version. `NEW_FEATURE` for components and variants, `BU
 Enum constants, catalogue data, building blocks and uncommenting. Cheapest fidelity per hour in
 the roadmap, and where D6 and D7 send most of the work.
 
-§6.1, §6.5 and §6.6 are correctness fixes and should go first regardless of the rest; §6.6 also
-gates §6.7, which is the channel the composable parts travel through.
+§6.1 and §6.5 are correctness fixes and should go first regardless of the rest.
 
 ### 6.1 Restore the `ElectrolyticCanCapacitor` alias — **bug, not a gap**
 
@@ -416,38 +416,14 @@ value-based auto-sizing, not a live fault.
 
 **~3 h including the test.**
 
-### 6.6 Make factory building blocks reach existing users — **bug, and a prerequisite**
+### 6.6 Make factory building blocks reach existing users — **done**
 
-Per §5.4, `importDefaultBlocks()` runs once per installation and never again, so every factory
-building block this roadmap proposes would land only on fresh installs. D7 routes most composable
-parts through that mechanism, so this is a prerequisite for §6.7, §7.5 and §8.9, not a nicety.
-
-Two ways to fix it, in `BuildingBlockManager`:
-
-**Recommended — drop the guard.** Delete the `DEFAULT_BLOCKS_IMPORTED_KEY` check and let the
-existing merge run on every start. The merge body already skips any name the user has
-(`if (!blocksMap.containsKey(entry.getKey()))`), so user blocks and user edits survive untouched and
-new factory names simply appear. Leave the flag being written so a downgrade still sees it.
-
-One behavioural cost, which should be a deliberate choice rather than a surprise: a user who
-*deletes* a factory block gets it back on the next launch. Mitigate by recording deleted factory
-names in config if that turns out to annoy anyone — not before.
-
-**Thorough — mirror the variant watermark.** Copy `VariantManager.importDefaultVariants()`: a
-`defaultBlocksImportDate` watermark plus a per-block `createdOn`. The obstacle is that `blocks.xml`
-is a `Map<String, List<IDIYComponent<?>>>` and `BuildingBlock` — which *does* have a name field but
-is not used in the stored format at all — carries no timestamp. Adding one means changing the shape
-of the `BLOCKS_KEY` config value, which also holds the user's own blocks. That is a config-format
-migration for a gain the simpler option already delivers.
-
-Take the recommended option. Extend `BuildingBlockManagerTest` (8 tests, `diylc-core`) with a case
-asserting that a second `importDefaultBlocks()` on a config that already has the flag set still
-picks up a newly added default name. **~3 h.**
+Factory blocks carry `createdOn`/`deletedOn` behind a `defaultBlocksImportDate` watermark; see §5.4.
 
 ### 6.7 Ship the first factory building blocks
 
 Data, not code, and per D7 this is where composable parts go. Each is authored in the app and lifted
-into `blocks.xml`. Gated on §6.6.
+into `blocks.xml`; each gets a `createdOn` later than the newest one already in the file.
 
 | Block | Built from | Why |
 |---|---|---|
@@ -458,7 +434,7 @@ into `blocks.xml`. Gated on §6.6.
 | Strat / Tele / LP harness | `guitar` pickups + pots + switch + jack | `guitar` components appear in only 8 of 425 files, which may be discoverability as much as demand |
 
 Author the push-pull pot first: it is the one with measured demand, and it is the worked example that
-proves D7 before the rest follow. **~2-3 h each once §6.6 lands.**
+proves D7 before the rest follow. **~2-3 h each.**
 
 ---
 
@@ -596,20 +572,18 @@ joins the §6.7 list rather than this one once someone asks for it.
 |---|---|---|
 | 1 | §6.5 six malformed datasheet rows, plus the validation test | 3 h |
 | 2 | §6.1 alias fix, verified by regression run | 2 h |
-| 3 | §6.6 factory building block import guard | 3 h |
-| 4 | §6.7 push-pull pot block, as the D7 worked example | 3 h |
-| 5 | §6.2 revive three, decide on the fourth | 3 h |
-| 6 | §6.3 UX4, then UX5 / B8G / B9D | 6-8 h |
-| 7 | §6.4 datasheets, `RadialCeramicDiskCapacitor` first | 6-10 h each |
-| 8 | §6.7 remaining blocks: transformer symbol, treble bleed, tube gain stage, harnesses | 2-3 h each |
-| 9 | §7.1 `Transformer`, with §7.3 Choke as its third type | 20-24 h |
-| 10 | §7.2 Speaker, physical plus symbol | 10-12 h |
-| 11 | §7.4 Footswitch | 10-12 h |
-| 12 | §7.5 `Photoresistor`, then the Vactrol block | 6 h |
+| 3 | §6.7 push-pull pot block, as the D7 worked example | 3 h |
+| 4 | §6.2 revive three, decide on the fourth | 3 h |
+| 5 | §6.3 UX4, then UX5 / B8G / B9D | 6-8 h |
+| 6 | §6.4 datasheets, `RadialCeramicDiskCapacitor` first | 6-10 h each |
+| 7 | §6.7 remaining blocks: transformer symbol, treble bleed, tube gain stage, harnesses | 2-3 h each |
+| 8 | §7.1 `Transformer`, with §7.3 Choke as its third type | 20-24 h |
+| 9 | §7.2 Speaker, physical plus symbol | 10-12 h |
+| 10 | §7.4 Footswitch | 10-12 h |
+| 11 | §7.5 `Photoresistor`, then the Vactrol block | 6 h |
 
-Steps 1-4 are about a day and a half: both known bugs cleared, the building block channel unblocked,
-and the highest-demand composable shipped as data rather than as a class. Step 9 is the one that
-matters most.
+Steps 1-4 are about a day and a half: both known bugs cleared and the highest-demand composable
+shipped as data rather than as a class. Step 8 is the one that matters most.
 
 Three items that looked like components when this roadmap started are now data (§6.7, §7.6, §8.9),
 and one is split into a primitive plus a block (§7.5). That is D7 working as intended; expect the
diff --git a/diylc/docs/plans/chassis-enclosures.md b/diylc/docs/plans/chassis-enclosures.md
index 7bf77c97..4eb6ea25 100644
--- a/diylc/docs/plans/chassis-enclosures.md
+++ b/diylc/docs/plans/chassis-enclosures.md
@@ -119,10 +119,6 @@ top by about 22 mm).
 - HWCHAS walnut-frame chassis (HWCHAS1310 / 1710; aluminium top 298.45 x 222.25 / 400.05 x
   222.25 mm on a 19.05 mm walnut frame): a different construction from the folded sheet metal.
 - Hammond rack cases (RM, RMCS) and the 1458 instrument enclosure.
-- Factory building blocks are still imported once, behind the boolean
-  `DEFAULT_BLOCKS_IMPORTED_KEY`, so a block added to `blocks.xml` later never reaches existing
-  users. Fix by giving factory blocks `createdOn`/`deletedOn` and an import date, as `VariantManager`
-  does, when a new factory block is next needed.
 - Configs older than class-keyed variants store keys like `Electro-Mechanical.Chassis Panel`;
   `VariantManager`'s upgrade maps them by the current category and name, so such variants would
   not carry over. Map the legacy name if it turns out to matter.
diff --git a/diylc/pom.xml b/diylc/pom.xml
index 545b68d1..9e9a27ee 100644
--- a/diylc/pom.xml
+++ b/diylc/pom.xml
@@ -140,8 +140,9 @@
                     <artifactId>maven-surefire-plugin</artifactId>
                     <version>3.2.5</version>
                     <configuration>
-                        <!-- XStream reflects into JDK collections when reading update.xml; mirrors the run configuration -->
-                        <argLine>--add-opens java.base/java.util=ALL-UNNAMED</argLine>
+                        <!-- XStream reflects into JDK collections when reading update.xml, and into fonts when reading
+                             import-defaults/blocks.xml; mirrors the run configuration -->
+                        <argLine>--add-opens java.base/java.util=ALL-UNNAMED --add-opens java.desktop/java.awt.font=ALL-UNNAMED</argLine>
                     </configuration>
                 </plugin>
             </plugins>