Quote: If someone is to send an offer (and I hope they're trustworthy!), I'll give them the code to test if it works or not. Test it out and respond please!

You can test if a code is redeemed on the console's dashboard. When you enter the code on the dashboard, and if it is not redeemed yet, the dashboard will show a confirmation popup to download the content, otherwise it will show an error message that the code is already used. There you MUST press B to cancel the process, and the code will not be redeemed.

But DO NOT try this on xbox.com! The website will always redeem the codes without confirmation, so it can't be used to test if a code is redeemed or not.