I wasn't aware BA.com sold non BA marketed flights? Can you give an example?
EDIT: just to add the trade partner advice for BWC/FTV says the following:
When does this apply?
...
These conditions apply to tickets issued on British Airways (125), for any carrier routing
Rebooking with credit valid for travel (outbound & inbound) by 30 September 2023 or EMD (RSVT) for future travel valid on:
- BA through fares and/or marketed routes
- Combined BA routing with SJB, AJB, Qatar JB
- IAG partner fares o SJB, AJB, Qatar JB and IAG partner routes/fares
- BA*MN (Comair) operated flights, either domestic within Africa or in connection with a BA operated mainline flight
- BA routings which includes Sunair, only if the routing is in connection to/from a BA mainline flight
Other carriers issued tickets may have different rules