diff --git a/frontend/src/lib/timeline/eventClustering.spec.ts b/frontend/src/lib/timeline/eventClustering.spec.ts
index c0419c02..f469f1c9 100644
--- a/frontend/src/lib/timeline/eventClustering.spec.ts
+++ b/frontend/src/lib/timeline/eventClustering.spec.ts
@@ -13,7 +13,7 @@ const makeEvent = (overrides: Partial<TimelineEntryDTO> = {}): TimelineEntryDTO
 	makeEntry({ kind: 'EVENT', type: 'PERSONAL', documentId: undefined, ...overrides });
 
 describe('eventClustering — buildEventLookup', () => {
-	it('maps each curated event (kind EVENT + eventId) to its title across years + undated', () => {
+	it('maps a curated year-band event to its title, excluding undated-bucket events (#7)', () => {
 		const timeline: TimelineDTO = {
 			years: [
 				{
@@ -25,8 +25,11 @@ describe('eventClustering — buildEventLookup', () => {
 		};
 		const lookup = buildEventLookup(timeline);
 		expect(lookup.get(EV_A)).toBe('Ein gewaltiger Stadtbrand');
-		expect(lookup.get(EV_B)).toBe('Briefe von der Front');
-		expect(lookup.size).toBe(2);
+		// An undated event renders as a plain pill in the undated bucket — out of clustering
+		// scope. Including it here would scatter its dated letters into orphaned ✉ cross-year
+		// cards detached from the pill (#7), so it must NOT enter the lookup.
+		expect(lookup.has(EV_B)).toBe(false);
+		expect(lookup.size).toBe(1);
 	});
 
 	it('ignores derived events (no eventId) and letters', () => {
diff --git a/frontend/src/lib/timeline/eventClustering.ts b/frontend/src/lib/timeline/eventClustering.ts
index 3b2e7e62..22e3ee78 100644
--- a/frontend/src/lib/timeline/eventClustering.ts
+++ b/frontend/src/lib/timeline/eventClustering.ts
@@ -29,6 +29,10 @@ export interface SplitLetters {
  * life-events and letters do not, so they never enter the lookup. HISTORICAL events are excluded
  * too: a world event always keeps its full-width WorldBand and never clusters, even with linked
  * letters (REQ-014) — those letters stay loose.
+ *
+ * Only year-band events are collected: an undated event renders as a plain pill in the undated
+ * bucket (out of clustering scope), so including it would scatter its dated letters into orphaned
+ * cross-year cards detached from that pill (#7).
  */
 export function buildEventLookup(timeline: TimelineDTO): Map<string, string> {
 	const lookup = new Map<string, string>();
@@ -40,7 +44,6 @@ export function buildEventLookup(timeline: TimelineDTO): Map<string, string> {
 		}
 	};
 	for (const band of timeline.years) collect(band.entries);
-	collect(timeline.undated);
 	return lookup;
 }