My Sailor Moon TV Anime Series Timeline Theories
(A)The TV Anime Series Timeline
Season-1 : Year-1. Usagi is 14 and the 2nd Year of Junior High School.
Season-2 : Year-2. Usagi is physically 14 and mentally 15 (because of her Wish at the end of Season-1). She is in the 2nd Year of Junior High School for the second time (However, because of the Wish/Reset, only Usagi and her friends themselves know this)
Season-3 : Year-3. Usagi is physically 15 and mentally 16. She is in the 3rd Year of Junior High School.
Season-4 : The first Neherenia/Dead Moon Circus battle actually takes place in Dreamspace (in realtime terms, it all takes place during the Eclipse in the first ep of Season-4, according to this part of my theories). So it is actually still Year-3, even though the Inners, mooncats and co all end up with about an extra year's worth of memories.
Season-5. Year-4. Usagi is physically 16 and mentally 18 now (She and the Inners, cats, Mamoru, etc now having two 'extra' years worth of memories, compared to the age of their current physical bodies). She is in the first year of High School. The second Neherenia battle takes place in Dreamspace yet again (IMO, this is takes place during the night the Mirror Shards supposedly fell, in realtime terms). The battle against Galaxia takes place in realtime.
(B)The manga, the anime movies spinoffs, the TV Live Action series, the Musicals, etc, all take place in their separete canon timelines and are AU to each other. (Though their is a possibility that 'Ami-chan's first love' could fit into the TV anime timeline).
(C)The anime Crystal Tokyo we see in Season-2 is not actually the direct future of the TV anime main timeline. (They wouldn't have been hit that hard by the Dark Moon Family/Wiseman if it had actually been the same timeline, for example)
(D)The first Dreamscape Battle against Neherenia took place either right before or right after their High School Exams for real (not the practice exams mentioned in Ep122). IMO, it was probably right before - that's why some of them were still worried about studying, even while they were stuck in Dreamspace.