So they actually don't weigh the plates before competition? Wow! I assumed there would always be an official scale at any legit meet to weight all the plates to get an exact weight...
Yeah, on the calibrated sets, it's generally thought ok, because they are guaranteed by the factory, and it would be an expensive thing to try and fake. The sets themselves running into the high 4 figures for the size need to run a meet.
With meets run on gym plates it can be a tough thing, as someone always forgets to weigh them, or weighs them long before or long after the lift. It wasn't uncommon in the old days to have a lift be a decent bit over or under weight. A famous case of plates not weighing what they should happened to a powerlifter named Ernie Hackett. He was set up for a #903 squat, and when they weighed out everything it was #940.
Then you've got the meet directors. Usually most guys just take their word for it, but some times you'd get whispers that meet director x has a few special lighter plates that they let lifter y use during the meet, etc....
