I wouldn't blindly take a code somebody got from a friend of a friend and try to book a room with it.
You need the entire advertisement or blurb or postcard that describes the rules and conditions.
You don't want to arrive at the resort and suddenly find out you need an annual pass or need to answer some questions in Spanish (RE the Spanish newspaper's ad) to check into the room.
You get postcards based on Disney's profiling of you, either from past visits or from information Disney got from banks, insurance companies, credit card companies, etc. because you did not opt out after reading the latters' privacy and information sharing notices.
Disney hints:
http://members.aol.com/ajaynejr/disney.htm
I would expect, that if you failed to fulfill the code requirements you would either get the room at the best discount you did obviously qualify for such as AAA or AARP, or be given a refund of your deposit to walk away.