There was some timeline confusion about the flashback, partially based on two previous instances of the gym uniforms of Yuki and her classmates indicating they are second year students.

Piro speaks:
please understand that the numbers and letters on Yuki's gym uniform should not be considered canon. back then, you could hardly accuse me of having the time line worked out fully, and my lack of understanding of the details of how demarkations of the japanese school system at the time didnt help either.
you people think too much. I'll simplify it for you. flashback yuki: first year of middle school. flashback miho: last year of middle school. 2+ years ago.
Now stop hurting your brains. This all reminds me of the rediculousness with which classic literature is analized. Ya, sure, the people who wrote this stuff deliberately put all that crap in there. Much of it, sure - it's just amazing how post rationalization of real life events can be used to give an ordered rational to what at the time was organic in its creation.
its a human trait to do this, so i go with it. Just dont hurt yourselves. MT has plenty of glitches. So does life, you can't explain everything you know.