Originally Posted by number_6
1) Don't know but I believe Sabre (AA's reservation system) cannot contain a PNR with no AA segments, in which case AA cannot store the PNR for you. The airlines can force you to ticket with the airline flying the first leg (presumably BA in your case) but generally don't. AA may refuse you unless you fly either trans-Atlantic or trans-Pacific on AA.
I'm ignorant about codeshare protocols, but 2 of the 3 daily BA flights from WAW to LHR carry AA codeshare numbering. If you ticket for those but then don't fly out of LHR on AA metal or another AA codeshare flight, does that negate the "AA-ness" of the WAW-LHR segment?
It would be helpful, Jonny, if you would give us an idea of your overall itinerary.