diff --git a/Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBPageMapReconciliationCoordinator.swift b/Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBPageMapReconciliationCoordinator.swift
index 03b85e8..c601bfe 100644
--- a/Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBPageMapReconciliationCoordinator.swift
+++ b/Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBPageMapReconciliationCoordinator.swift
@@ -164,6 +164,7 @@ final class RDEPUBPageMapReconciliationCoordinator {
         lastBuildableSpineIndex: Int
     ) -> RDEPUBPageMapTakeoverDecision {
         let candidateIndices = Set(candidatePageMap.entries.map { $0.spineIndex })
+        let currentIndices = Set(currentWindow.entries.map { $0.spineIndex })
         let currentEntries = currentWindow.entries.count
 
         if let currentSpineIndex {
@@ -189,8 +190,8 @@ final class RDEPUBPageMapReconciliationCoordinator {
             }
         }
 
-        let isComplete = candidateIndices.count >= currentEntries
-        if isComplete {
+        let coversCurrentWindow = currentIndices.isSubset(of: candidateIndices)
+        if coversCurrentWindow {
             RDEPUBBackgroundTrace.log(
                 "Reconciliation",
                 "evaluateFullPageMapTakeover: fullReplace — candidateChapters=\(candidateIndices.count) currentChapters=\(currentEntries) candidatePages=\(candidatePageMap.totalPages) currentPages=\(currentWindow.totalPages)"
@@ -198,6 +199,10 @@ final class RDEPUBPageMapReconciliationCoordinator {
             return .fullReplace(candidatePageMap)
         }
 
+        RDEPUBBackgroundTrace.log(
+            "Reconciliation",
+            "evaluateFullPageMapTakeover: keepCurrentWindow — candidate does not cover currentWindow candidateChapters=\(candidateIndices.count) currentChapters=\(currentEntries)"
+        )
         return .keepCurrentWindow
     }