Xbox Redeem Codes Recycled?

I just wanted to know how the xbox redeem system works, and if Microsoft recycles previous codes?

For the record I'm not trying to scam, I just came across a guy giving out beta codes for Gears3 but when I searched the codes a number of websites appeared.

I would be shocked if they ever re-used a key, ever.

An Xbox key is a 25 character long string which can take letters or number. It does not differentiate uppercase from lower case.

The number of possible combinations is thus: 24+10⁽²⁵⁾ or 10³⁸.

To give you an idea of how big of a number this is, there are an estimated ~10²³ stars in the universe. If each of those stars had 1 planets around them, and each planet was inhabited by 1 billion people, and each person could redeemed 1 million codes before they ran out of codes.

For Xbox to reuse codes they would have to implement an entire second system to recycle codes with 0 actual benefit.

I think it's a very safe assumption to say Xbox does not reuse codes.