We could still have nine seasons in the 90s anime even if the movies weren't counted, namely, Dark Kingdom, Rainbow Crystals (a sub-season), Makaiju, Black Moon, pre-Hotaru S, Hotaru S, Dead Moon, Nehellenia, & Stars.
We have to divide SuperS into the Amazon Trio and Amazoness Quartet sub parts
For fun, you could also use the Openings to divide them lol
Classic - 3 parts - Moon/Mercury/Mars Trio, Jupiter/Rainbow Crystal, Venus-Princess Serenity
R - 3 parts - Makaijyuu, Ayakashi/Rubeus/Chibi-Usa, Crystal Tokyo/Demand and co.
S - 3 parts - UraNep/Kaolinite, Eudial/Search for Grail, Super Sailor Moon/Hotaru
SuperS - 2 parts - Amazon Trio, Amazoness Quartet
Stars - 2 parts - Nehenelia, Galaxia
Which plus 3 movies makes 16!
Anyways, I divide the Crystermos adaptation by production cycle.
Crystal I & II as one, Crystal III as a second and Eternal and Cosmos as the third (since we know they began production as soon as the movies hit theaters and there was literally no change since Tadano didn't even create new setteis at all).
Basically by character design, the Sakou era, the Takahashi era and Tadano era.