FBA Missing Inventory Proof of Ownership Request (NEED EXPERT ADVICE)

I’m a small volume used video game seller. I had a shipment of products delivered to Amazon a few months back. They were held up for extra processing and now are showing as discrepancies. I have a saved email showing that Amazon confirmed this shipment was received in full from late August. At this point, I can now put in a missing product request but I need to submit documentation. Obviously, selling used video games means obtaining them from locations like garage sales, flea markets and game stores. Before submitting game store receipts, I was hoping to get some advice on what has worked best in the past.

Thanks in advance for the help!