How long will a USPS tracking number remain valid?

The records of mail classes and services, including access to package history and Proof of Delivery when available, are stored in the system for the life of the package data:

What if my item was received, but not scanned as delivered?

The absence of a delivery scan on a mailpiece does not necessarily indicate that the item was not delivered. It is possible the piece was delivered but the scan was not captured. If you think this has happened, you may wish to contact the sender or recipient to confirm delivery of the item.

If there are no delivery scans in our system, and you know the package was delivered, the sender can request a partial refund for the USPS Tracking product (but not the postage). 

What to do if I think the tracking information is innacurate?

Mailform retains information about tracking via the USPS API and in some cases, we keep this information beyond the USPS package data lifespan indicated above. This means that it is possible the USPS webpage shows stale or empty tracking data, while we have kept a confirmation of these events.

To get confirmation about proof of delivery from the USPS directly - customers should contact the USPS.