3) Japanese television series
Japan does not have television seasons like the US does. However, Sailor Moon was divided into several different series, each aired weekly and lasting a year:
Sailor Moon: 3/7/92-2/27/93 (episodes 1-46):
The appearance of the five Sailor Scouts and their fight against the Dark Kingdom.
Sailor Moon R: 3/6/93-3/5/94 (episodes 47-88):
pisodes 47-59 have as villains two space aliens Earl (Alan) and Ann. 60-88 are a fight against the Black Moon family, also introducing Chibi-Usa (Rini), a young girl from the future. Sailor Pluto first appears (but only briefly) here. Episode 89, 3/12/94, was a special (and a clips episode).
The only explicit reference I got for the meaning of the R is from the Sailor Moon Memorial Song Box: "R wa ROMANCE ya RONDO, RETURN nado, samazamana kotoba wo imi suru mono to sareteiru." ("R is intended to mean various things like ROMANCE, RONDO, and RETURN.")
Sailor Moon Super: 3/19/94-2/25/95 (episodes 90-127):
Villains are Professor Tomoe and the Witches 5 (the Death Busters). Chibi-Usa first becomes Sailor Chibi-Moon, and Sailors Uranus and Neptune first show up (and later Saturn).
Sailor Moon SuperS: 3/4/95-3/2/96 (episodes 128-166):
Villains are the Dead Moon Circus and Nephrenia. Heavily based around Chibi-Usa. The Outer Senshi don't appear at all except in an (unnumbered) special.
Sailor Moon Sailor Stars: 3/16/96-2/8/97 (episodes 167-200):
The first 6 episodes (167-172) finish off Nephelenia and are often considered the real ending of SuperS. After that, a new storyline begins with the villain Galaxia from Shadow Galactica, whose henchmen are Iron Mouse, Aluminum Siren, Lead Crow, and Tin Nyanko (the Sailor Anima-mates). Heavy Metal Papillon was another, appearing only in the manga. Introduction of the Sailor Stars, who are male in normal IDs and change to female as Sailor Senshi. Introduction of Chibi-Chibi, an even younger kid character. Chibi-Usa doesn't appear at all except for cameos, and Tuxedo Mask shows up in 173 leaving for Harvard, and then not until the end. The Outer Senshi appear sporadically.