Thanks for the detailed explanation. Just one more Q, if you don't mind:

What would the AA RTW Desk tell me if I tried to have them set up this ticket for me for an ex-JP (say) RTW origin? D9 or D0?

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.

Well, I am not really sure what you meant by "central point". Every booking source (including the AA RTW desk) is associated with a certain city/country code. So, if you know that for a particular flight, availability for a US-based POS is better, then yes, it would be to your advantage to book through a source that meets that criteria ...

By 'central' I meant a point not associated to any specific country of origin except, of course, the country where the central point is located (USA in this case), working on the assumption that a US-based POS is [possibly?] the least likely to suffer from these capacity controls. Another benefit from this approach is the better synch between what the AA RTW desk sees and what half-blind tools like EF show (I was impressed by the 'view both options' capability of the KVS Tool).