You can't simply check the keys when I 1 already own the game, and 2 even if I do activate the code it will promote mt to download the game with no indication whether the code is duplicated or whatnot. Therefore you cannot simply 'check' if the key is fully working. Now if there is some sort of programme that checks the keys availability if it has been used and the game itself ect then I will use that. I. But I haven't come across anything like that before.