I made this post last week about a pack not being delivered and figured I would update as I finally managed to pick it up. Turns out the vendor did absolutely nothing wrong as far as the address label goes. Label was printed and all the information was there, including the apartment number. For some reason the mailman marked it "undeliverable as addressed" fucking twice in a row. The first time, I was a day late getting to the post office to pick it up, but when it made the loop and got sent back to me a second time, I went in a few hours after the failed delivery and picked it up no problem. The guy at the post office was even really confused as to why it didn't get delivered.
Bottom line, USPS fucking sucks donkey dick sometimes and is very susceptible to human error. However, I think their cluelessness helps us in the long run for the most part. Also, don't be so quick to blame vendors. They're people too.
Thanks for update. Glad it worked out