The striping actually is redundancy -- it's a redundant ordering indicator for the deck. The nominal ordering is ... the card order. But should that be disturbed, the stripe (a diagonal marking across the edge of the cards) will indicate which cards are out of sequence.
I first encountered this trick in a college library with a physical card catalog. Having been pranked once too often by students re-arranging the drawers, the fronts of the catalogs were crossed with multiple bands of different colored tape. Any out of sequence drawers could be immediately noticed and quickly sorted visually.
