It isn't complicated or opaque. Imagine you are a CGC distributor. Do you want to give your customer list to PPS? Certainly not. And since we want to sell backglasses only to CCR owners, we will do this via the distributors. And yes, we will limit the number to the number of games. So distributors will only be able to buy from PPS a number of backglasses equal to the number of games they are ordering from CGC (which we *can* verify without knowing customer names).
Simple, right? Every customer can buy a backglass from the distributor from whom they bought a game. Think of it as an (optional) perk for buying a CGC game.