Dumb question about the Sailor Moon timeline

Hi, I've been watching Sailor Moon for a few years, but I've always wondered about one thing:

In the final events of the first season, Sailor Moon destroys Queen Beryl, and then all the senshi's memories, including her own, are wiped. However, I've read quite a few people online saying that, additionally, everyone was sent back in time a while, so that the girls had to start 8th grade over again. What?

I don't recall it ever been said in the series that the girls were sent back in time, but it does explain why they were in 8th grade for two seasons, Classic and R. So, the time-jump would be a good explanation, except that the girls were also in 9th grade for two seasons, S and SuperS. There was no significant time jump in those seasons, so I've always ran with the assumption that each season of Sailor Moon takes place over roughly half a year. So, Classic would take place over the first half of the year, and R would take place over the second half.

My explanation is also backed up by the fact that, in the beginning of Classic, Usagi is wearing her long sleeved school uniform, and when the girls leave to teleport to the North Pole at the end of the season it's clearly quite cold out, so it would seem that Classic takes place through Fall/Winter.

But still, I see many people on websites talking about the girls starting 8th grade over again, and so I'm doubting my own logic. Is there something obvious I'm missing, or are these people crazy? I'd be grateful for any help.

Thanks.