What happens if you have two bookings, for the same passenger, on the same flight? Or more specifically, what is the procedure for ensuring that you don't have two bookings for the same passenger on the same flight, i.e. after a cancellation of one ticket when you then rebook on the same flight?

I would say "apropos of nothing", but... As I posted a couple of weeks ago, I lost and then luckily had my passport returned to me at LHR. Full details in that thread, but - to the best of my knowledge - the original ticket's return leg from BSL to LHR was cancelled and used instead as a 'coupon' (I'd love to understand how this works) to get me from LHR-MAN on that day. So I didn't think anything of, when I booked new travel arrangements via the BA website a few days later, choosing the return leg from BSL-LGR on the same flight and date as my original (now cancelled) ticket.

But it occurred to me that if for any reason, that ticket was somehow still active, there would be two people with my name and personal details booked on the same plane (quite possibly in the same exit row). This seems like the kind of thing that might raise some eyebrows.

Within Manage My Booking, the original PNR is still showing the original BSL-LHR leg on the same date/flight as the new booking. However, this original PNR is also showing the plethora of other flights I did (and didn't) take on that booking, as described in the earlier thread. So is this a red herring?

Is there a way for me to confirm that the original ticket is completely cancelled (ideally without spending ages on the phone to BA)? Or is this totally unnecessary because it doesn't matter either way?