Originally Posted by Schultzois

One of the key parts of that thread (which I would have thought might have been pointed to, since 25,000 Miles plus availability doesn't necessarily point to an upgrade being allowed under these circumstances:

I had also remembered a travel agent who could do upgrades with BA explaining to me that one thing they cannot do is upgrade any portion whatsoever of an itinerary that involved non-BA flights. So if a reason for buying at AA.com is that there is a leg or two on AA (often the case when I buy BA fares at AA.com) then if what I'm told is true, regardless of who I bought it from, it seems like it would be non-upgradeable. I think I once had a BA phone agent tell me basically the same thing (for the same itinerary, as it happened). In the end, since the one-way fare difference between D and A was only $750, I just paid the A fare anyway (even though the majority of the itinerary didn't offer a FIRST product in the first place, which is what got me thinking I'd just pay for Club and upgrade the applicable leg).