Reading this with interest as my trip last week had a missed IB/BA codeshare connection due to the first BA flight being delayed, missed flight needed rebooking.

Initial rebooking by BA was for a day later, they never asked me if this was ok and there was no good reason as there were two later flights available same day: one was another IB/BA codeshare, the second an IB with no BA codeshare. Eventually got re-rebooked on the non-codeshare IB flight (with my BAEC number showing on the boarding pass).

The first leg has credited, but not the second. BA certainly knows about the second one as it was listed as a choice in the online compensation form that I completed for the late arrival at final destination. Guess I'll wait a few days and see what happens. I've kept all the BPs so I have the e-ticket numbers.