mox: You wrote “If more chools where discoved by more experrienced survey there would consistently be more 6th, 7th, and 8th graders in the second study than there are 1st 2nd 3rd graders in the first (as they are the same class) this is not the case (at leasr with regard to yeshivish)”
However you answered your own question when you asserted earlier “schools with only a few grades are more likely to be missed”
These new small schools discovered in the second survey only have younger grades and account for the disproportionate increase relative to the older classes.