Re: Question for Dave D
Rob, AJ is correct. But to answer your last question more completely: discs from opposite sides could have differences due to being shipped across country. East coast discs undergo multiple temperature and pressure changes before they arrive in Carolina. The little stickers you see on Candy discs now, are placed there to prevent a more drastic change that used to happen to these discs during shipping.
By far, the most important part of any shot is what is happening in the last split second as the disc is pulling itself from your grip. Focus there. It's the key.