I guess it could be changed to
series major
series minor
but would be minor benefits to it, as it would use about the same space in the database.
Also noticed there's anthologies or volumes/collections (books 1-2 or books 1-3 of a 20+ series) .. for example see Argeneau series (scroll to bottom):
https://www.goodreads.com/series/40687-argeneau
And there's also short stories ... some label it as SS1, SS2 (Short Story 1 etc), others use series 1.0a , 1.0b ... a, b, c ... for short story.
Some use the decimals for short stories or a mix (ex .1 for short story, .5 for small novel) , for example Psy-Changeling series by Nalini Singh :
https://www.goodreads.com/series/41454-psy-changeling