Originally Posted by
Tyrolean
Nope, they don't. They use two different AMADEUS systems. You can figure it out that Flights with QF and BA Segments have usually two Filekeys: One for BA and one for QF. Usually you can assign seats with the corresponding Filekeys in each website.
Really? Maybe it used to be that way, but a couple of weeks ago I flew BA and QF on a single ticket, and it was same PNR for both BA and QF -- I just checked to confirm this, so definitely the same filekey. Seats were visible and assignable on both ba.com and Qantas.com so it looked pretty seamless. I used ba.com to change the Qantas.com initial seat assignment and all was well. Both seemed to work equally well and I didn't notice any anomalies, but I wasn't looking for problems.