I’ve ordered from Amazon recently and sometimes I’ll receive a USPS tracking number that doesn’t work when used on the USPS Website, even though the info was updated within Amazon itself. The answer to this problem is very simple. The items aren’t actually being shipped the entire way via USPS. Sometimes they’re sent most of the way via FedEx. If you plug the same tracking number into the FedEx Website you will probably find the most current info.
When items are shipped this way they can be tracked via FedEx until they reach your local post office.