If you say it is authentic then why wont it pass TPA? They will authenticate items that they did not witness, that is their job. Unless it is fake that is the only reason they wouldn't be able to.
On some items they give a no opinion which is not a pass or a fail. They have failed plenty of real items, and passed plenty of fake ones it happens all the time. Unfortunately all it is is paying for an opinion. Dont get me wrong it adds value but they are not always right about everything they pass or fail