LOL at this and your other comments in this thread.
I dont know one way or the other but I would imagine that if a girl cheats with an XXL then goes back to a XS boyfriend, the guy would be able to know. I say this because if me and my g/f go at it several times in short order, it isnt quite the same the next day. Maybe Im not quite filling up 100% of my unit, or maybe she is a bit loosened up, but it isnt as good.