Just to circle back on this (in case anyone else sees this issue in the future), BA had a couple of attempts at fixing this, including re-ticketing it. Still nothing got updated in AA, and all that was there was the ticket header (ie AA knew I had a flight, had my name and booking number, but no other details).

In the end it took a 3 way call with both BA and AA on the line to get resolved. They don’t really know what the issue was, but the BA customer support agent said she’d seen this a couple of times before…

Glad I spotted it, as I wouldn’t have been able to check in on those flights otherwise.