I think with stylized heads I have a harder time spotting mistakes as sometimes they can have some weird intentional stuff that defies logic XD especially anime, I mean, sometimes they have brows that surpass the limits of the head, mouths with lips that disappear and become a triangle etc etc and it's all just part of the artistic language of that style and well, nothing wrong with that
On these what I do note is sometimes the head is getting bigger or smaller, on 9 I think the forehead is cut back, there is variation in the character's jaw width you can easily tell by comparing 2, 4 and 10 for example, also the chin is changing size and width a bit but this seems like a nice practice to try to get a character down from multiple angles