Earlier quoted context omitted.
Unless you know every other digit in the card number, I don't see how knowing the luhn algorithm is going to narrow the possibilities of guessing just the two digits.
Also credit card can never be used by itself for any purchase, ever. You must have the name, expiry date, and if you're doing transactions online, often the address and ccv2 as well.
More than likely you dont need the name or cvv, sometimes not even the expiry.