337.171 isn't that high a mark when CRGS is your only viable option, and it's in the orange zone, and you KNOW that isn't a true mark of his abilities due to illness.
The school will mark the papers for you. I'm not sure what is wrong with your son, but it sounds like you have solid evidence for an appeal, should he not make it. Sorry, when I posted the other day I'm sure you had said 37?. With that score you wouldn't need to worry.
Any child sitting an exam in need of surgery is obviously not going to do his best. I think you have a good chance anyway.
Over the years I have heard of a few mishaps with marking, but not many. I have heard of candidates being swapped, but that was a long time ago. I have also heard of marks changing by one mark, but rarely.