The amount was under $500, so the company decided it was not worth pursuing. Neither us nor the vendor know who the person is. The address they changed it to was also near the original destination, so it's possible, if it wasn't one of their employees, USPS misdirected this piece of mail.

We are going with the assumption the check was either stolen from the mail, or misdirected by USPS.

The vendor sent me a 2yr AR report which included these two "outstanding" invoices, but only asked about the recent coming due. I'm taking this as a sign that they don't want to push it, and hoping that I just pay it, with out them saying anything.