The changelog line is about the trigger itself: it’s stored durably and repaired automatically after an outage.
For the calls themselves, a webhook call that waited longer than its time-to-live during an outage isn’t run on its own. It goes to Failed messages with the reason “Waited too long”, and Replay runs it. Replay keeps the original ids, and the outbound blocks send the same idempotency key, so if the system you call deduplicates it sees the call once. Details in Protections and failed messages.