I haven't checked all boards, obvs, but I think they have to know their school grade for NEA as the only personal appeal opportunity is to the school before the school submits. (So they see the marked essay as well as the score).
The exam boards review a selection of the school's entry to confirm the grades, so the mark shown to pupils by the school is only preliminary. If the. Board disagrees with the marking of the selection of papers they review, the whole cohort is marked down accordingly.
The school can appeal but they have to appeal the whole year at once, with the usual up or down risks, so I can't imagine that happens very often - surely all pupils would have to consent? Has anyone heard of such an event (just curious).
I think DS2 gets his marked english NEA back tomorrow. Thankfully he has forgotten this so isn't fretting :-) I feel slight dread- the whole business was a tad gruesome, as he did entire drafts for two abandoned questions before settling on his final choice, all while preparing for a pointless English exam entrance test back in October ish.