Specifying a single artist would exclude circles from the tag.

One "volume" of a Manga series, often containing several chapters or sections of the story.

I’m of the opinion that a description or definition should not include the word being described/defined.

Collected or completed volume, comprising various stories by the same author and artist

I agree that the definition should include something about the work having a single artist.

ehwiki describes as "A complete book by a single artist published by a third party" and notes that incomplete galleries do not qualify, so something like "A complete book by a single artist published by a 3rd party, must be complete"

maybe add to the description something to discourage the usage of the tag for incomplete volumes, it muddies the waters.