There's no seat number on Ryanair anyway.
At a minimum usually mine gets checked twice
once to get thru security - sometimes you can jump this one if you have the correct itinerary paperwork stuff
and once just before heading down the jetway or onto the tarmac for the walk out to the plane. This is normally where the pass and the stub part company. You can't jump this one normally.
Some airlines check again on entering the plane.
It's not a great system but it does work most of the time since any alternative costs so much it would be unworkable.