Re: Why keep so much info?
If you read the article, you might also have spotted the point that some of these clubs are set up to cater to military vets, and offer discounts to the same. So before offering you half off on your drinks, the business should verify that you actually served.
Still doesn't explain why they would keep the license or such on hand afterwards, but I do understand why they would need this information (providing it should be voluntary, obviously - you might well think that your privacy isn't worth the discount even if you *are* a vet).