Godfather movies not a series?

I saw on the page for The Godfather movie (can't find touchstone) https://www.librarything.com/work/643664 that the movie, Godfather, Part II is listed as a non-series sequel. Now I don't really care if this is listed as a series or not, but it seems to me that The Godfather movies parts I, II, and II are indeed a series and I was just wondering why it was listed as a non-series sequel. They are often sold as a set! Does someone know something I don't?

And now there's a new version of Pt III

>2 Crypto-Willobie: There's a new version of Part III?

>1 al.vick: That's weird! Maybe someone didn't know how to make a series and that was their best solution? Anyway, I've removed the work-to-work relationship and made a series for the films. https://www.librarything.com/nseries/326455/The-Godfather-%7BCoppola%7D

>3 al.vick:
https://en.wikipedia.org/wiki/The_Godfather_(film_series)#Recut_version

>5 Crypto-Willobie: Ahh...I was unaware of the "recut" of III. Good to know.

I saw a bit of it on the tee&vee last night...