I'm so bad with telling apart girl groups.
Twice I know because of Sixteen. But Red Velvet, I can name Irene only.

Lovelyz has Kei and Jisoo, and I think I know Eunji from APink? Lord help me if my life depended on knowing all the Cosmic Girls by the end of the year.
Agencies better see the influx of ginormous girl groups and keep debuting small-membered groups like BlackPink. (I'm aware that Pledis Girlz will be releasing another 10+ girl group and that just blows my mind. :skull)