Well, I looked at CAS adult screen when buying clothes, it seems to be several random outfits from different XP/SP. Remember wrong and thought the adult section showed the outfits the premade YA sims using like Blossom Moonbeam's crop top/maxi skirt outfit, but it wasn't there.
Weird, I thought I had the ones that hides the kimonos, apron from base game.
Blurry but attached a picture of all maxi outfits the hiders didn't take. The only ones that suppose be there are the military outfits which is unlocked versions, but doesn't have custom icon for some reasons.
EDIT: Yep, the YA maxi clothes seems to be in the right category after all. Now I'm just wondering if it's possible to hide them consider they only appear in th CAS screens at Uni, but I don't create students...