I'm not sure that it matters as I still haven't grokked what the see tombstones on key fold flag is for, but: we always skipped values that have already expired (new line 366 above), but if they happen to pass that test (about to expire on near second boundary), have the same size as a tombstone, and then expire by the time we call get(Ref, Key), they will be returned as tombstones whether they really were a tombstone or not.