Most of it is, I'm happy to tag the relevant stuff. But other artists do occasionally create "in universe" art (off the top of my head, Caroo, Blue Coffee Dog, JedaySkayVoker, DefilerZero) or sometimes art of their RD OC getting into some sort of situation.
I don't think a series tag would work as there isn't a cohesive set of rules or consistency. To the point, I've even had the artist specifically ask me not to make a Wiki on it (I was joking when I suggested that, TBH buutt..)