My question is this: Is there any mileage in blaming the school?
No, I don't think so, because you have little need of extenuating circumstances with scores of 120/119.
I have absolutely no doubt your case will simply depend on sufficient academic evidence of high ability. http://www.elevenplusexams.co.uk/appeal ... cation#b11
However, I agree there's a risk that the '1' recommendations may look 'devalued', so I suggest you tackle this head on by referring very briefly
to the fact that the school has been through a difficult period. "Of DD's classmates only ~15% passed and only 50% of those the head graded as 1. This is compared to the school's pass rate of 30 - 50% in recent years.
I got the numbers slightly wrong yesterday: Of the 1,1 recommendations the head made only 50% passed, none of the 1,2s (inc DD) none of the 2,1's and one 2,2.