diff --git a/documentation/features/bookdate.md b/documentation/features/bookdate.md
index 88a46c0..03fc762 100644
--- a/documentation/features/bookdate.md
+++ b/documentation/features/bookdate.md
@@ -449,6 +449,26 @@ Personalized audiobook discovery using OpenAI/Claude APIs. Admin configures AI p
   - User with autoApproveRequests=true auto-approves (status: 'pending', sends approved notification, triggers search)
   - User with autoApproveRequests=null checks global setting
 
+**10. Empty ASIN Matching All Library Books**
+- Issue: All AI recommendations incorrectly matched to first library book, causing empty recommendation list
+- User Experience: "BookDate returns 0 recommendations. Logs show AI generated 20, but all matched to 'Murder Your Employer'"
+- Impact: Critical - BookDate completely non-functional, all recommendations filtered out
+- Cause: Empty ASIN in database query matched every record in library
+  - AI generates recommendations without ASINs (title/author only)
+  - `isInLibrary()` calls `findPlexMatch()` with `asin: ""`
+  - Database query: `{ plexGuid: { contains: "" } }` returns all 29 library books
+  - Code checks: `plexGuid.includes("")` returns true for first book
+  - All 20 recommendations matched to same book → filtered out as "already in library"
+  - SQL behavior: `WHERE plexGuid LIKE '%%'` matches all rows
+- Fix: Add guard clause to return null if ASIN is empty or falsy
+  - Early return prevents database query with empty string
+  - First `isInLibrary()` call (no ASIN) → Returns false immediately
+  - Recommendation matches to Audnexus → Gets real ASIN
+  - Second `isInLibrary()` call (with ASIN) → Correctly checks for exact match
+  - Only books actually in library get filtered out
+- Files updated: `src/lib/utils/audiobook-matcher.ts:44-61`
+- Documentation: `documentation/fixes/asin-matching-fix.md` - Phase 3 section added
+
 ## Related
 
 - Full requirements: [features/bookdate-prd.md](bookdate-prd.md)
diff --git a/documentation/fixes/asin-matching-fix.md b/documentation/fixes/asin-matching-fix.md
index b985cd0..28d2011 100644
--- a/documentation/fixes/asin-matching-fix.md
+++ b/documentation/fixes/asin-matching-fix.md
@@ -511,4 +511,82 @@ This fix resolves the critical ASIN matching issue for Audiobookshelf by impleme
 - **Preserves critical functionality:** Fuzzy matching kept for Prowlarr torrent ranking
 - **Improves performance:** O(1) indexed lookups replace O(n²) string comparisons
 
-**Status:** ✅ Both phases complete and production-ready
+**Status:** ✅ All phases complete and production-ready
+
+## Phase 3: Empty ASIN Guard (January 2026)
+
+**Status:** ✅ Implemented
+**Date:** 2026-01-28
+**Issue:** Empty ASIN causing all library books to match AI recommendations
+
+### Problem Statement
+
+**BookDate Recommendations Returning Empty:**
+1. AI generates 20 recommendations (without ASINs)
+2. BookDate calls `isInLibrary()` to filter out books already in library
+3. `isInLibrary()` calls `findPlexMatch()` with empty ASIN (`asin: ""`)
+4. Database query: `{ plexGuid: { contains: "" } }` matches ALL records (29 books)
+5. Code checks: `plexGuid.includes("")` returns true for first book
+6. All 20 recommendations incorrectly matched to first library book ("Murder Your Employer")
+7. All recommendations filtered out → User sees 0 recommendations
+
+### Root Cause
+
+**Empty string matching bug in database query:**
+- SQL: `WHERE plexGuid LIKE '%' + '' + '%'` matches every record
+- JavaScript: `anyString.includes("")` always returns true
+- Prisma: `{ contains: "" }` returns all rows in table
+
+### Solution
+
+Add guard clause at start of `findPlexMatch()` to return `null` immediately if ASIN is empty or falsy.
+
+**Implementation:**
+```typescript
+export async function findPlexMatch(audiobook: AudiobookMatchInput) {
+  // Early return if no ASIN provided (prevents empty string matching all records)
+  if (!audiobook.asin || audiobook.asin.trim() === '') {
+    logger.debug('Matcher result', {
+      MATCHER: {
+        input: { title: audiobook.title, author: audiobook.author, asin: audiobook.asin },
+        candidatesFound: 0,
+        matchType: 'no_asin_provided',
+        matched: false,
+        result: null,
+      }
+    });
+    return null;
+  }
+
+  // Existing ASIN query logic...
+}
+```
+
+### Expected Behavior
+
+**BookDate Flow (After Phase 3):**
+1. AI generates 20 recommendations (no ASINs)
+2. First `isInLibrary()` call with empty ASIN → Returns `false` immediately ✅
+3. Recommendation matches to Audnexus → Gets real ASIN
+4. Second `isInLibrary()` call with real ASIN → Correctly checks for exact match ✅
+5. Only books actually in library get filtered out ✅
+6. User sees 10-15 new recommendations ✅
+
+### Files Modified
+
+**Matching Logic:**
+- ✅ `src/lib/utils/audiobook-matcher.ts:44-61` - Added empty ASIN guard clause
+
+**Documentation:**
+- ✅ `documentation/fixes/asin-matching-fix.md` - Added Phase 3 section
+- ✅ `documentation/features/bookdate.md` - Added to Fixed Issues
+
+### Benefits
+
+1. **Fixes critical bug:** Empty ASIN no longer matches all library books
+2. **Prevents false positives:** Only exact ASIN matches are considered matches
+3. **Aligns with design:** ASIN-only matcher requires valid ASIN to match
+4. **Single-line fix:** Minimal code change with maximum impact
+5. **No breaking changes:** All existing functionality preserved
+
+**Status:** ✅ All three phases complete and production-ready
diff --git a/src/lib/utils/audiobook-matcher.ts b/src/lib/utils/audiobook-matcher.ts
index 15fb39f..61ad68e 100644
--- a/src/lib/utils/audiobook-matcher.ts
+++ b/src/lib/utils/audiobook-matcher.ts
@@ -41,6 +41,25 @@ export interface AudiobookMatchResult {
 export async function findPlexMatch(
   audiobook: AudiobookMatchInput
 ): Promise<AudiobookMatchResult | null> {
+  // Early return if no ASIN provided (prevents empty string matching all records)
+  if (!audiobook.asin || audiobook.asin.trim() === '') {
+    logger.debug('Matcher result', {
+      MATCHER: {
+        input: {
+          title: audiobook.title,
+          author: audiobook.author,
+          narrator: audiobook.narrator || null,
+          asin: audiobook.asin,
+        },
+        candidatesFound: 0,
+        matchType: 'no_asin_provided',
+        matched: false,
+        result: null,
+      }
+    });
+    return null;
+  }
+
   // Query plex_library directly by ASIN (indexed O(1) lookup)
   // Check both dedicated asin field and plexGuid for backward compatibility
   const plexBooks = await prisma.plexLibrary.findMany({