The game value isn’t technically restricted to those listed. Most unlisted won’t have any and most of the ones that do are typos of the game directory entry. See https://api.twitch.tv/kraken/clips/top?game=Counter-Strike+Global+Offensive&api_version=4 vs. https://api.twitch.tv/kraken/clips/top?game=Counter-Strike:+Global+Offensive&api_version=4 (notice the colon)