In the pre- game coach/official meeting the officials ( umpire usually) asks the head coach if all their players are legally equipped (yes is usually the answer) and if anyone has a piece of equipment the officials ( umpire) need to check for legality. At that point the officials are off the hook......or that's how it was when I was officiating before retiring.

Dangling mouthpieces will soon be addressed similar to towels and streamers hanging from the waist. Mouthpieces  will be required to be attached to the helmet and individual mouthpieces will be illegal. This will be controversial similar to the rule change that made single bar face masks illegal and the change that all chin straps be 4 point snaps