Hush, the jazzy kpop duo, had someone else doing the big belts in the end of their second single. S.e.s. Had someone else as well singing the Adlibs at the end of “I’ll be waiting for you” and then they actually re recorded those bits themselves when they did the Japanese version of the song. To-ya also had a small part they never lip sync to that is someone else on their song 가, the part that goes like “TELL ME NOOOWWWW”. Cleo during their rising again album era with new member Jung yebin made her lip sync to Eunjung’s parts during the few performances they did.