If the order is important, then a series pool is justified. The problem is that the pool description does not say anything about this. The current description makes it sound like a random collection of in-game artwork. Nothing about it implies there’s any order to them. And not all users will understand what is meant by “traditional game CGs.” If these are scenes from the story, the pool description should make it clear. If they need to be in a certain order and it’s not obvious how to order them, then that should also be explained.
Whether this pool stays or goes, a tag would still be useful for distinguishing story art from other game cg posts.