The marker initialisation code creates and installs markers, and then refreshes the markers to account for concurrent inserts. This refresh samples the last RecordId, and updates the highest wall time and RecordId, but does so without modifying byte and record count (code ref).

Partial marker expiration depends on either record count or byte count being greater than 0 (ref).
This means that any entry accounted for in the refresh will not be dropped even if the wall time and RecordId are correct (in the absence of new inserts).