I purchased (from Wal-mart) a few years ago .... a Muscle Machine that was the commerative 9/11 Series. It says "69 Camaro" on the front label, but the car is a cuda (with all cuda labeling) did this happen on purpose? Or is this a rare find, package has never been opened and card is in VERY good condition...

It is simply an error package. Rare? Yes, probably. However, there are very few people who collect error packaging on Muscle Machines. Therefore it probably has very little value. Things are only worth what people are willing to pay. If you can't find someone who collects MM errors, then you probably won't find anyone who even wants it, let alone pay for it. The only error car collectors I have heard of only collect Hot Wheels errors.