The numbers on the back - the CVV code - is essentially a cryptographic hash of the information on the front of the card: expiration date, name, card number, wh

The numbers on the back - the CVV code - is essentially a cryptographic hash of the information on the front of the card: expiration date, name, card number, whatever else is on there. So each physical card should have a different CVV if the card number is the same. Given 3-4 digits and millions of issued cards, there will of course be collisions among cards with different numbers. I think every card issued by Visa, Mastercard and American Express (at the very least) in the US has these extra numbers.