Did some speedrunning to get to reset2 and reset4 for the sole purpose of checking if any other parameter is dictating the number of ✓ on the wall with my limited knowledge about renpy; and the results are underwhelming as expected
The only player choice that has an effect on it is
your decision with Ami. As far as I check, other meaningful choices we can make does not have an impact. I.e., manipulating flags like sarasex, harukasex, makisex, rinbetrayed, yumiknows, karinlied, or anything related to skipping Ayane/Kirin toxic scenes will not change anything.
(an afterthought is that I should've just checked how many varying versions of corkboard source images there are as it's a much faster solution

; and of course there are only two for each reset, 3 or 4 for reset2 and 6 or 7 for reset4)
What's a little different is that in reset2 it checks ami_virgin and in reset4 it checks amifingered. The inconsistency is probably just Selly maybe forgot what parameter he used for checking as story-wise it makes no difference.
And I can safely say ✓ is not just counting towards how many v-cards. Excluding Ami, girls with virgin flags are Ayane/Makoto (true at reset2), and Chika/Kirin (true at reset4); this means a maximum of 3 and 5 at different resets, so nope! Forcing these flags to change won't do anything as these are hard-scripted and unavoidable.
Conclusions? still don't know too much about anything

.
The only thing we know is pursuing Ami counts, and we don't even know
why it counts with 100% confidence. It's easier to exclude what matters not than narrow down what matters.