Hannibal and orbitmic, thanks for pointing me in the right direction. The threads you reference do not seem to have reached any sort of consensus -- BA guru jerry a. laska seems to think that no miles are due, since it was marketed by US, whereas others think that the operating carrier is the decisive factor.

I jumped on the phone with BA and they seem to think that I would get Avios/TP as AA is the operating carrier as long as I give AA my BA#.

However, it looks like this means I can give US my A3# and double-dip these miles -- as can anyone flying a US marketed/AA operated itin before 31st March. If so, that's a pretty big deal, no?

In any case, I'll report back at the end of March to let y'all know what posts.