diff --git a/connectors/google/src/calendar/google-api.ts b/connectors/google/src/calendar/google-api.ts
index 1284db5d..cc85b0f0 100644
--- a/connectors/google/src/calendar/google-api.ts
+++ b/connectors/google/src/calendar/google-api.ts
@@ -91,10 +91,26 @@ export type SyncState = {
   min?: Date | null;
   max?: Date | null;
   sequence?: number;
-  // Initial sync runs two passes: "quick" (timeMin=now, front-loads upcoming
-  // non-recurring events and future exceptions) then "full" (timeMin=history
-  // limit, picks up long-running recurring masters excluded by the quick
-  // pass's timeMin). Undefined on incremental webhook-triggered syncs.
+  // Initial sync runs two passes: "quick" (timeMin=now) then "full"
+  // (timeMin=history floor).
+  //
+  // The quick pass front-loads everything upcoming, recurring series
+  // INCLUDED: Google does not apply `timeMin` to recurring masters. Verified
+  // against a live calendar — a FREQ=YEARLY master whose first instance was
+  // in 1980, and a FREQ=WEEKLY master whose RRULE `UNTIL` had already passed,
+  // were both returned by a `timeMin=now` listing. Only non-recurring events
+  // are actually bounded by `timeMin`.
+  //
+  // So the full pass is NOT what makes recurring meetings appear (an earlier
+  // version of this comment claimed it was). It exists to import past one-off
+  // events and to establish the `nextSyncToken` that incremental syncs reuse.
+  //
+  // Do not generalise this to Outlook: Microsoft Graph's
+  // `$filter=start/dateTime ge …` is a literal comparison against the series
+  // master's own (first) start, which genuinely does exclude a long-running
+  // master. See `outlook/src/calendar/sync.ts`.
+  //
+  // Undefined on incremental webhook-triggered syncs.
   phase?: "quick" | "full";
 };
 
diff --git a/connectors/google/src/calendar/sync.test.ts b/connectors/google/src/calendar/sync.test.ts
index 06c10b10..1f47a6d5 100644
--- a/connectors/google/src/calendar/sync.test.ts
+++ b/connectors/google/src/calendar/sync.test.ts
@@ -11,6 +11,7 @@ import type { Thread } from "@plotday/twister";
 import type { CalendarSyncHost } from "./sync";
 import {
   buildEventSources,
+  calendarHistoryFloor,
   cancelEventWithApiFn,
   cancellationWasSelfInitiatedFn,
   extractRSVPParamsFn,
@@ -2148,3 +2149,18 @@ describe("processCalendarEventsFn — initial-sync occurrence round-trips", () =
     expect(totalRoundTrips(large.calls)).toBeLessThan(10);
   });
 });
+
+describe("calendarHistoryFloor", () => {
+  it("is exactly 366 days before now, so annual events stay in window", () => {
+    const now = new Date("2026-08-03T12:00:00.000Z");
+    const floor = calendarHistoryFloor(now);
+    const days = (now.getTime() - floor.getTime()) / (24 * 60 * 60 * 1000);
+    expect(days).toBe(366);
+  });
+
+  it("keeps an event dated exactly one year ago inside the window", () => {
+    const now = new Date("2026-08-03T12:00:00.000Z");
+    const oneYearAgo = new Date("2025-08-03T12:00:00.000Z");
+    expect(oneYearAgo >= calendarHistoryFloor(now)).toBe(true);
+  });
+});
diff --git a/connectors/google/src/calendar/sync.ts b/connectors/google/src/calendar/sync.ts
index 4d04d5d9..622674c1 100644
--- a/connectors/google/src/calendar/sync.ts
+++ b/connectors/google/src/calendar/sync.ts
@@ -283,17 +283,15 @@ export async function firstSeenAtFn(
 }
 
 /**
- * Start of the history window the initial backfill imports: Jan 1 of two
- * calendar years ago (mirrors the `historyMin` computed when the quick pass
- * transitions to the full pass). Events scheduled before this were never
- * imported, so a cancellation for one can only materialise a phantom thread.
+ * How far back the initial backfill imports: 366 days — a year and a day, so an
+ * annual event is always inside the window. Events scheduled before this were
+ * never imported, so a cancellation for one can only materialise a phantom
+ * thread (see `cancellationIsForUnimportedEventFn`).
  */
+export const CALENDAR_HISTORY_DAYS = 366;
+
 export function calendarHistoryFloor(now: Date = new Date()): Date {
-  const floor = new Date(now);
-  floor.setFullYear(floor.getFullYear() - 2);
-  floor.setMonth(0, 1);
-  floor.setHours(0, 0, 0, 0);
-  return floor;
+  return new Date(now.getTime() - CALENDAR_HISTORY_DAYS * 24 * 60 * 60 * 1000);
 }
 
 /**