Pro Tip: Most people don't bother with the codes, and most of the games have expiration dates on their registrations that are out for YEARS.
I don't know how many used DS and Wii games I've gotten, gotten home, and registered the game, no problem. I honestly think maybe only one HASN'T worked.
I've gotten both of the Game and Watch Collection DS games and both of the sets of Zelda posters. Have also had Platinum status every year since they started the Gold/Platinum set up in 2009. And I've already gotten it for this year, so I'll hold onto the codes I get until July 1, when it resets. By July 10 (when they ask me to do the Post Play Surveys for the games I register on the 1st) I'll have Platinum again. Rinse and Repeat.