Just a heads-up, SG lets me enter this despite owning the game plus its DLC :/

double thxs!!=}

You need to check winner before sending game. FWIW even those who already have the game can still enter, and the game doesn't show in their library if you search for the game.

You will have to add the winner and then check it using "Friends that play":

Bottom line is that, SG cannot detect ownership of this game. Most likely an API glitch