Originally Posted by
FenLandK
I've done this for the situation as you describe, where you have AA metal flights booked through BA, but if I'm not mistaken the OP is saying that the situation is the other way round - they have BA metal flights booked on AA.com.
One of the reasons this situation could arise is because BA use Amadeus and AA use Sabre to manage their bookings. Some stuff connects, other stuff doesn't. After these systems have been around for so long, it still surprises me that they don't connect any better. In this case I think it's because AA "own" the booking that BA isn't allowing the change - much like a TA booking. It is interesting that AA isn't so rigid in the inverse situation; as you described, using the AA PNR will allow you to alter the seat allocation on aa.com. So it looks like BA's systems are the ones holding the OP back.
Sorry I had completely misunderstood the OP. I had thought it was a BA code booking on AA metal as you say, the OP was quite clear, I must have been having a senior moment last night
Presumably the way forward for the OP is to find the BA PNR (which BA will use to identify the trip in Amadeus). BA should be able to give this number to the OP and he should presumably then be able to use BA MMB correctly?