The iCal standard treats UID as a permanent identifier for an event. Booking.com's export does not, because what it exports is the set of unavailable nights, not reservations; when that set changes shape, the events describing it may be regenerated with fresh identifiers. Airbnb re-keys far less often but is not immune.
Lemon's rule 1: identity is (property, feed, checkout date), never the UID. When a tracked UID is absent from a healthy feed and the same checkout is present under a different, unclaimed UID, the new UID is adopted onto the existing booking and a rekey_adopted decision is logged. The cleaning job and its cleaner are untouched.
In the 30 days to 2026-09-10, 78 re-keys were adopted across 18 feeds — about 4.3 per feed per month.