Clerical Re-check?

I posted this in another topic, but I haven't gotten a response yet and I'd really like to hear what other people have to say before I start splashing out on a clerical re-check.
I'm thinking about getting clerical re-checks on a couple of OCR History papers (A2 level). I missed an A by 1 mark overall (479), with pathetic marks this year on both my exams. I got 77/120 on my US History Paper and 42/90 on my British. (Down from 90/90 on US Paper and 81/90 on British Paper last year, but that's irrelevant). However, I got photocopies of the papers back and the marks on my British History paper actually add up to 48 (10+20+18), not the 42 that my Results Statement gives! I know that they mess around with the numbers a bit after they're marked (most of the time they seem to give you a couple more points thatn you actually scored), but I seem to have been docked SIX marks off what I actually scored! Is this usual or has it happened to anyone else? Considering I missed an A by 1 mark, it seems highly unfair that my mark should have been altered in such a way. Luckily it didn't damage my University place, Nottingham took me even though my offer was AAA and I technically only have AAB, but it's still annoying.
Any thoughts would be much appreciated, thanks.

Dude snap, messed up one paper and I had 78/120 when I got the photo copy the raw marks added up to 78/90 dunno what thats all about

I read all about the UMS conversion, but why do they need to screw around with my marks?
I did 3 modules, 2 out of 90 and 1 out of 120. I scored 48/90 and 76/120 on the two exams and 80/90 on coursework. That's a total of 204/300, if they simply added them up. Instead of doing that however, they gave me 42/90 and 77/120 on the 2 exams and gave me a total of 199/300. What purpose does converting a mark out of 90 to one out of something else serve, when it needs to be out of 90 for the final score?