It totally depends on what "release" means in the context. The concept of the English word is overlapping the ones of the Japanese words 発売, 発表, 公開 or 公表. For instance, when a song has already been performed in a concert but hasn't been on sale yet, the song is 既発表曲 / 既公開曲, but not 既発売曲. It's 未発売曲.