How many ask to be reviewed by the exam board? Loads (but under 50% of the cohort). We are a very academic selective private school with pushy parents- if there's a way to get a higher grade, they'll know about it and we will take it!
But requests for the HoD to 'just have a look at the paper first' just in case? Yeh, hundreds. Honestly hundreds. HoDs have been literally inundated by requests to look over papers 'just in case' in previous years. Even if they probably wouldn't be going for a review, they ask anyway, as they like the reassurance that nothing was missed. And if you say yes to one, you obviously can't say no to the others!
To illustrate the issue: say if there's over 160 pupils in a cohort - 2 exam papers for that subject (maybe 4 if it's English if they don't do the coursework route for IGCSE) - that could be potentially hundreds of exam papers for HoDs to look at. Up to 600+. And word spreads, so at least half the year want their papers relooking at by their HoD (word spreads fast through the parent and pupil whatsapp channels). In a cohort that size, even if only half as the HoD to take a look, that is easily 300 papers! I used to to have to send my kids on holiday with my husband without me, while I spent the whole week after results' week ploughing through them, hours and hours a day. It wasn't as bad for opinions subjects, but awful for core subjects where all students took the exam. HoDs hated it and some considered quitting over it. I myself thought about quitting over it!
Thankfully our SLT are sensible and said it had become ridiculous. Staff at my school are the most hard-working I have ever met, and have bags of goodwill, but this was breaking us before term even started. SLT would much rather retain their staff: we're the most sought after independent school in the area and excellent staff are the most important factor in that. There was talk of a possible admin fee to put people off, but we felt that would just lead to further complications (plus parents would see it as an expected service then - and a tenner is not going to really put anyone off when they're paying more than £25k a year for fees!) and besides, despite many of us being very experienced examiners, our opinions often bore no correlation to what actually did or didn't change so it was a waste of time anyway in most cases!
So yes, they go in blind. And no grades have gone down. Last year my subject had almost two dozen grade increases. I looked at precisely zero papers before the review requests were submitted. We've already had grades go up this year too. Seems to be working for us 👌
(PS I do agree with you about the educational inequalities though. I was a very deprived, FSM child myself. But there are far bigger educational inequalities than this. If you want something to be really mad about, it should be the fact that private school kids can do IGCSE with coursework.... that is REALLY not fair!)