That's okay, you don't have a full picture and I'm probably not explaining it well.
There are different types of pieces, balls are but one of them. Each piece type can have a variation in one of well-defined styles: plain, striped, glass. Each style has one spritesheet associated with it, which covers every rotated state, up to 12.
Inside of the game, each available style for each piece corresponds to a unique kind of foil pack. E.g. you have a pack of striped balls.