Strictly from the POS perspective, if AA RTW desk (located in DFW) requests availability for the flight in question, then they should see D9 (since their POS country would be US).
However, BA can use other criteria as well -- here is a partial list:
http://www.Amadeus.com/airlines/x7394.html
Understood that there can be other criteria, but it seems then that one viable way to get around this problem is to deal with a central point (like the AA RTW desk), since the availability
for them is not tied to the country of origin where the ticket is eventually being issued.