Topic: I feel like "vulva" and "vagina" should be separate tags.

This is because the vagina is actually not part of the vulva. It is the muscular tube that connects the cervix to the labia minora. The vulva is what you see on the outside, except between the labia minora.

A lot of the time that people use the term "vagina", they mean "vulva". And since the vagina itself is rarely depicted on its own, having vagina be a separate tag (or be disambiguated) would end up needing to replace it with vulva more often than not.

You're thinking of vaginal_canal.