School have recorded my absence as unauthorised when they authorised it

So I get study leave like next week but after Easter I decided that it's be best if I work at home between then and study leave and go in when I need to go in as I get distracted easily in class and basically all the teachers finished teaching the courses so all we would be doing is revision in class anyway.

Anyway, the school agreed to this and stated that I could just go in when I felt I needed to come in and I have come in a few times.

Today when I was in I asked one of my teachers to look up my attendance marks on SIMS and I looked at the dates I've been off over the past week and one day they marked me in as S which means study leave and is a present mark then most of the time they've marked me in as N which means no reason provided for absent and D which means I never provided a reason for absence, they are both unauthorised absence codes.

The irony of it is the school authorised my absence and said that this was fine so I'm pretty sure they should have marked me in using code O which means other authorised circumstances. What do I do about this?