The Expanse is the name of both a series of novels, and the TV show based on that book series. They both share one tag, the-expanse. Is that OK? Should they be split up? If so, how?
(In addition, the two first books have their own tags that I have proposed to merge into the-expanse; leviathan-wakes and calibans-war, respectively. This should probably only be done if the master tag shouldn't be split, I guess.)
Currently policy is generally that all individual works get their own individual tag. Some exceptions apply, such as films or books of a series (similar to how each episode of The Expanse will not get its own tag). So, there's not a need to tag Caliban's War individually, which Gallifreyan's answer also addresses, unless the question is truly about events self-contained within those books or the book itself (such as writing it, behind the scenes, analysis, etc.).
Some pre-existing popular tags, like Harry Potter, do not have a book and film distinction because they have been grandfathered in due to the sheer magnitude of work involved in adjusting the tags. But, in general, we shouldn't penalize a written work because a TV or film version of it happened to be produced without changing the title Legend of the Seeker or Game of Thrones style.
The general format is the original media gets the plain tag:
And the same named works in whatever media get the initial year of release appended to the end, so the TV series would be:
That is what I would normally recommend doing in case there's already questions about one or the other (or a question about both and adaptation-comparison.
However, to make it more clear, I would prefer the-expanse-novels and the-expanse-2015 to avoid mistagging show questions with the book tag.
In order to accomplish this with the least disruption, we need to:
Anything and everything that is both a book and a movie should have separate tags. Neither of which should consist solely of 'the name' of the saga, because the users who are going to misapply tags aren't going to read tag descriptions.
I answered a LotR question once and a commenter's response was, "Who cares about the movies?"
I don't think we need separate tags for TV series and the novel series in this particular case.
In case a distinction is needed, askers are free to clarify the medium by supplementing their questions with tv or books, respectively.
We should probably add a section to the tag usage guidance, explaining that the appropriate medium tag should be used with the-expanse.
Regarding the merging part, I don't think this should be done. According to this answer separate books are more or less self-contained, and could be read separately and out of publication/chronological order. This implies that people might be asking questions related not to the universe in general, as it most often happens with LotR or ASOIAF, but related to specific book.
