Remember, the SQA are trying to cut the number of appeals because the process is so lengthy and a bit of a pain in the bum for them, so if a candidate misses out on the grade he/she was predicted, they look at the grades that the rest of the class got and try and bump the grade of that candidate up accordingly.
So, say Candidate A was predicted a B but got a C in the exam, the SQA look at the rest of the class - what they were predicted and what they got in the final exam and if the rest of the class basically got what they were predicted by their teacher, Candidate A would get his mark bumped up to a B.
The candidates never know this, but the teachers get a little list telling them who has been graded this way.