What slips through
The cancelled order that was refunded to a card you no longer check. The return the carrier says was delivered back but the retailer never processed. The lost parcel where the claim window quietly closed. None of these announce themselves. You find out when you reconcile, if you reconcile.
Deadlines that matter
Retailers have return windows, usually fourteen to thirty days. Carriers have claim windows for lost parcels that start from the expected delivery date, not from when you noticed. Card providers have chargeback windows too, which are the last resort when a retailer stops responding.
Keeping it visible
One list of everything owed, with the amount, who owes it, and the date it should have landed by. No typing it all in by hand. Anything past its date gets flagged, and anything that lands gets ticked off.
Minted members get this as the refund tracker, alongside their orders, so "is that refund in yet" is a glance rather than a search.