Sadly, mail forwarding by the USPS is not reliable. It might work in smaller communities but it seems to be a totally manual system that does not work in larger communities. When I sold my house and wanted the mail forwarded to my mail handling service in South Dakota, the Post Office could not make it happen. I visited the post office 3 times but the mail just kept being dropped in my old box even after we moved out and there were new home owners.
Eventually a major piece of mail with a large check was not forwarded and was eventually returned to the sender. I found out a couple of years later when the IRS sent me a notice that I filed incorrectly and owed a major amount of capital gains.