Thank you so much! How far did you get? because after the first page basically all the other levels have + and -
I see! that's because the last level on each page is a bonus with certain conditions to be met to unlock (hinted by the lack of star requirements but only ???) also there is a blinking arrow on the right of the screen as soon as you have enough stars to have unlocked another level in the next page, I hoped this fixed the misunderstandings but it seems that's not the case :(