jyp lost lily m, yg recently lost isabella I think
youha debuted in 2020, and sua will be debuting with mystic rookies
I kept up the most with sm's female trainees, pretty much everyone who was there since 2016 have left already, I think I can name around 15: hyorin, eunjun, chaehyun, sera, jungmin, koeun, lami, hina, rjing, plu, jungyeon, yejin, jiyeon, jihyeon, etc
edit: you always know when a new group is in the making when a bunch of the older trainees leave