My parents will be flying AUH-LHR-DFW in CW/J this Saturday, with the AUH-LHR on BA and LHR-DFW on AA. The BA flight is booked as the AA codeshare, and the ticket was issued by AA on 001 stock. I did call the AA EXP desk to have them give me their BA record locator, and using that I can access their reservation through MMB on BA.com.

However, I noticed that MMB does not allow me to even pay to select seats when I go to Seating. For the BA flight, I see the following message:

"Seat selection will be available on this flight when your e-ticket is issued"

For the AA flight, I see:

"Seat choices are available at check-in"

I am not worried about the AA flight, as I already have seats selected for them through AA.com. I am however somewhat concerned about the BA flights. I was planning to OLCI and select seats for them at T-24, but the "selection available when e-ticket is issued" message is slightly concerning. I do definitely have an e-ticket issued, which I confirmed with AA.

Will this prevent me from OLCIing them? Does anybody have experience OLCIing BA flights when issued as a codeshare, or on another airline's ticket stock, or with other airlines on the same record?

Thanks!

Edit: I should add that my parents are currently BA blue, though this itinerary will take them to Silver.