Thanks for the reply:
1. For DFW to MAD (non stop) on Iberia when booked through AA I see C7 on EF when choosing AA for business upgrade, non stop. hence I got confused.
AA (IB) 8631 DFW MAD Aircraft 333 C7 on May 21, 2025
But AA 36 non stop DFW MAD U0 C0 on May 21, 2025
2. Sorry, I didn't understand BA 1504 (operated by AA) so it is AA then like AA51?