I understand that GSX no longer asks for passenger numbers for deboarding. If I had skipped the boarding passengers stage at departure, what passenger numbers are used if I wanted to watch them deboard at the destination?
More precisely, it skips the request for the number passengers on Deboarding if you used GSX on Boarding, so GSX already knows how many passengers you have, this regardless if you input their number manually, or use the "Estimate" option so, if you had Estimate disabled, if you didn't specify anything and just pressed "Enter" on the request, it would use the same figure as if the Estimate was enabled.
This behavior was clearly an improvement we added following user suggestions that always want to remove useless interaction. In this case, we assume the number of passengers on arrival won't change compared to how many departed, so it's not requested again, which would be only useful to cover fringe cases, like somebody dying or somebody being born during the flight. Sure, it can happen, but is very rare and won't grant forcing an extra question that is useless in 99% of the cases.
If you really want a chance to indicate the passenger arriving after you already used GSX on departure, the easiest thing to do is to "RESTART COUATL" anytime before the arrival, so the number used on departure will be reset.