I'm not entirely sure! This trip started off being from Gatwick, then BA changed that to Heathrow. I did nothing to confirm that change to keep my options open. Now the Heathrow flight has been cancelled and rebooked to the following day. The ticket number is different from the original Gatwick one but I don't know if another ticket would have been issued when the original change to Heathrow happened.

Looking at the return flight, which has not been cancelled but has moved to Heathrow and which I have not confirmed, it seems (from Finnair) that the original Gatwick ticket number is still "current" so the move to Heathrow did not generate a new ticket number. Which suggests that the outbound cancellation and rebooking has generated a new number so all should be good.

Is that what you would expect? I don't have much experience of these things but have read enough horror stories of BA failing to ticket bookings that I wanted to be sure and the error message didn't seem a good sign.

Also, is there any way of finding an itinerary from a ticket number?