PBA: We don’t really need to come up with all the population growth info you are looking for as we have school data which is probably more accurate than guesstimating how many kids are average per family, figuring out over how many years etc.
And YW-95: the younger grades are probably a better indicator as some boys leave for overseas/Canadian Yeshivos, girls to seminary, and some kids may unfortunately drop out. (Probably more boys, but that’s my opinion.)
It’s also interesting that although he didn’t ask for gender information at special ed schools, and there are presumably more boys enrolled in such, the rest of the schools still have more boys. And even if this gender disparity is due to actual gender birth differentials, it’s still much less of a difference than the grade differential.