There is some inconsistencies in how tag names for various movies are created. This is to clear up how they should be named, based on existing examples. So here is my proposed approach for movie series and sequels:
Primary movies should be tagged accurately. It will also serve as the franchise tag, barring any weird examples (retconned names/retronym (Star Wars/A New Hope, Star Trek/Star Trek TOS) or unique franchise names (Marvel Cinematic Universe))
Secondary movies should be tagged as follows. If it is simply "Title Number" then tag it as such. If it is a complete title (ex: Batman Begins) then tag it as such. If it is "Title: Subtitle" where the title is the franchise name, and Subtitle is a unique name that the film is known by, drop the title.
A tag in the form of "Title Number" should not be created unless the movie is known that way. If it is created, it should be a synonym, and not the proper tag.
Recently, movies have been split into parts (for fun and profit), and named as such "Title: Subtitle- Part n". The prescribed tag method should be "Subtitle-n"
Any question on individual titles should have both the individual title tag and the franchise tag.