Missouri subscriber
Answer: One of our medical law experts says he would have a number of serious concerns about a policy like this. If a contractual payer is involved, there are most likely clear prohibitions against keeping or offsetting the overpayment, as well as giving discounts on the front end. Also, you should examine accounts with discounts and overpayments independently - not lumped together.
The HHS Office of Inspector General or state agencies could have fraud and abuse concerns about a policy that lumps accounts together and dictates indiscriminate action like this. Agencies may also question your discount policy if you also allow recovery of the discounts in the event of an overpayment.
Bottom line: A policy for recovering past discounts with current overpayments would have too many legal pitfalls. You shouldn't pursue this idea.