In Q&A under Receipts is a Question for finding Receipts (Customer Payments entered in the Receive Money tool) that have been Applied to future (post-dated) Invoices.
This Solution explains using this Q&A to find payments which are not properly records as prepayments or accidental errors causing problems auditing accounts receivable. (6184)
Open the Q&A tool from the InfoCenter toolbar or the File menu and select Receipts in the pulldown. Double-click on the Question:
"Which Payments Were Received and Applied After..."
On the dialog asking for a Date enter your cutoff date. This cutoff date will find all Receipts dated on or before your cutoff date that are applied, even partially, to an invoice dated after the cutoff date.