Bad Data - Bad Report (Score 0, Redundant)

I bought iTunes music for 2 years on my Visa. Then switched to my AmEx at the beginning of this year. I'm not saying our boy, Josh Bernoff, was looking at my credit card... But what exactly was he looking at and how much room for error is there when using 2000 credit card samples to determine a pattern out of 1.5 billion song purchases?