Thanks both, that seems OK. I'd hope that if bag didn't arrive in SJU at same time as we did, they would at least be there by the next day to check back to JFK!

Interesting about treating multiple inineraries as one. Which leads to another question.

We have already booked LCY-JFK, which means we arrive as "domestic" as immigration is done during refuelling at SNN - but want to go straight to BOS. Two choices (for AA), 1h 50 after arrival, or 5 hr. Probably different terminals as well (I believe BA arrive at T7, AA depart from T8). (Travelling First Class for the extra TP )

If we were booked on the earlier one, and BA arrived late, would we get transferred to the later one (its not the same booking, but they are both oneworld). Or would it be better to play safe and hang around for 5 hours.