I believe what you are referring to is one of the "Scam" clubs that publish a list of campgrounds that they compile off the internet. Then they market that list by saying they have a guidebook of over 10,000 parks offering, and this is the key phrase, "up to" 50% off.
Almost all the parks in the book never have heard of the club, never had any contact with them and offer nothing to their members. You will find a few parks that will honor it, simply because they will honor anything. That is how they get away with the scam.