I find that mathematics A-level incidents these days seem to be mirroring my university experiences. In my finals, I was faced with a seemingly straightforward question which I couldn't do. I now know that the reason was because it relied on a specific method from a first-year course which I hadn't taken, although I did not realise this at the time.
It's not easy to describe the panic that can result when you find you cannot do a seemingly straightforward question. In my case, I just received a bland statement that "there were other questions on the paper" that I could have done instead, which missed the point. When AS students talk about the effect on their futures, I do not consider that they are overstating the case.
It is hard to see how Edexcel can fairly adjust the results so that students do not suffer. We had similar "reassurances" when one of our exams was brought forward two weeks at the last moment. I could see at the time that these reassurances were worthless, and Edexcel's promises are probably worth just as much.
PS Didn't a similar incident occur in an AS maths exam last June?