Originally Posted by
Flying Yazata
Nope, that's a wrong assumption. The TATL sectors had to be AA by AA. And IB flights within IATA area 2. Those, who booked an AA by BA segment for a TATL sector, benefited from a system loophole, while that wasn't supposed to be doable as per the fare rules.
This is not a loophole. The rules are clear that you have to fly at least one AA or AA/ IB flight via Europe - if you figure out to get this the system will hapily reward you with an AA/ BA flight.