In bug 20815 we added the NoRefundOnLostReturnedItemsAge system preference to block lost item refunds if the item was lost more than X daya ago. Many libraries would like a comparable system to block refund if the lost item fee has been paid in full more than X days ago. Further, even more libraries have asked for the ability to simply not refund paid lost items at all (they only want to refund/forgive lost fees that are not yet paid). Enabling this new syspref to block refunds on lost items paid off more than 0 days ago would support this behavior.