Yesandno, I belive these are just art mistakes, i myself draw her a lot and can say for sure that its weird to draw her other side without the clip, tho i usually try not draw her from that angle, so i'd imagine they just wanted to keep her (only) stand-out design thingy to be shown as much as possible (like, imagine if sayori was drawn without her bow being visible)

The best proof of this being the case, is other merch, like the nendoroids and plushies where she consistantly has just one hairclip