UGCs are bigger than Genesis/Mega Drive cases. There is a noticeable difference in size in terms of height. The spine on UGCs are larger as well. I separated my CIB Mega Drive games and created my own custom covers for the loose carts I have. If you want to go retail and get the case sizes uniform, I recommend doing the same (separate the CIB games with the loose carts boxed in UGC). Alternatively, you could just look around for a seller selling Genesis's cases or pick up a bundle of sports games, take the cases then sell of the sports games and their manuals.
