Ah I'm fully aware that I had this game in my library so this is a spare key.
There should be no compensation involved I guess.
If winner already owned the game then it's with them and the system, it's no one fault, winner can just pass it forward, I encourage that.
For other duplicated key, if you put it in your Steam, Steam will say that you already owned the game and the key will still be redeemable without any issue.
Thank you for asking and sorry for the confusion this caused to you. ♥