*Comment. The subject is credited as "Choi Soo-young" for her various movie roles, as you can see at  HanCinema, allmovie, Rotten Tomatos, MySoju, and KMDb. In Korean, it's the same, as you can see here and here. I assume the "Girl's Generation Sooyoung" moniker is a promotional gimmick for the band. She can and does use a normal name when she appears independently of SM.