As of right now, I don't think that the "thru pax" thing is in effect for US to AA. Or, perhaps you have to prove it to them with a boarding pass?
On behalf of all of the mama's and papa's of our "almost combined" airline, can I please plead with everyone to be kind? I try my darndest to be nice to all non revs, I don't care where you come from, I mostly fly Intl, and now with AA rules, everything is free, but my smile and "there's an empty row over there-MOVE!" has always been free. At US, we had 10 years of serious famine, and all we had was eachother so we really tried to look after our own. Keep in mind, while our numbers have changed ,and our name is changed, we still have to look out for eachother!
I know that the agents have a ton of pressure on them, and nonrevs are a pain in the tucus, but that's my kid/ husband/ dad/ mom! Please, they're a little dumb, but please, please be patient! I've done my best to drill they bejesus out of them, but they're dumb passengers, and I will be so grateful to you for any kindness you show. I promise that I will do the same! I've arranged their "yeah right" upgrade if it happens, the rollover to my best ability! I don't even let them fly unless there's more than 20 seats available!
They better not hand you a coat and they will tell you that they're a nonrev before you do meal orders!
US agents have done such kind things for my family members, so I always try to return the cosmic favor. If we can all be kind to eachother, it won't matter who runs US at AA, we will win this game no matter the nonsense.
Just my 2 cents!