It said in the accompanying humph that if a boy is below qualifying standard he won't even be considered, which says to me that the qualifying standard must cover more than 150. I'll drop them an email and ask, at least it's not just me confused!
Correct, there is a qualifying standard which, to me, means they rank enough DC's to take up all Grammar School PANs, plus a few extra to compensate fot those who do not opt for a place. You cannot be considered for a place if DC has not reached the qs. You can put the school on your CAF application but your DS will be turned down for a place on the grounds that "he did not meet qualifying standard". You will then have to appeal on the grounds of non-qualification.
Marling does seem to have caused a bit of confusion this year - but no doubt they have told everyoe where their DS is on the list to try and minimise phone calls along the lines of "how far off a place is my DS?". Looks like it may have back-fired though