@Mytimenow - that's really annoying! I hope your DS wasn't too wound up by it.
Just to throw a spanner into the works about grade boundaries / grades - DS1 school said that the % of DC getting a grade 9 for each subject will vary from subject to subject.
This is because from some subjects (i.e. Ancient Greek and Latin) the DC who sit them tend to be more academic than the whole cohort of 16 year olds. So you will see a greater proportion getting higher grades in these subjects than for subjects where the cohort reflects the full range of ability (maths and English?).
I'm not sure how they make it 'fair' but that's what we were told!