Same here, I know because my grandson hasn't cashed the check and so I talked to him and they haven't received anything from us.
Talking to the post office folks is a waste of effort, the cards are in a black hole.
The Postal Service cannot find stolen mail. We hear about those mailbox stands, where multiple homes get their mail, getting broken into by vagrants multiple times a year and that is just the ones near enough to hear about. Multiply that by the number of those that exist all around the country and also apartment mail stations and you can get an idea of how easy it is to lose mail.