You can test the codes on Flixster or Vudu. Just make sure you're not signed into your account and enter the code. If it asks you to log in then the code is good, otherwise it will show that it has already been redeemed. :-)
The websites is being the being the biggest pain. I would like to say its the first movie that was used. But don't quote me on that. Sorry for this. Happy bidding :)