OWLs - still don't add up

[rolshan2000]

No: HPFGUIDX 133572

I appreciate how minor this is in light of the more earthshaking 
events and revelations in HBP (the best book yet, by the way, in my 
view; and I for one think the ships were beautifully done and very 
consistent with the foreshadowing in the prior books), but I still 
can't get Hermione's OWLs to add up.

We are told she got 11 OWLs, but she was only taking 10 classes - no? 
She was taking the same ones as Harry and Ron, as confirmed by their 
OWL test report, which were 9, minus Divination, makes 8, plus 
Ancient Runes and Arithmancy which makes 10. So how could she get 11 
OWLS? The theory that some subjects resulted in more than one OWL 
seems shot. I suppose it is possible Hermione took an OWL exam in a 
subject she was not taking at school (for example, she could 
obviously get an O OWL in Muggle Studies without taking the Hogwarts 
course) but it seems odd this would not have been mentioned!

Further, even allowing Hermione her 11 OWLs, we still don't know how 
the legendary students of the past (Bill Weasley, that boy who was 
selling study aids in OOP, etc.) ever managed 12 OWLs, without use of 
Time Turners.

Anyone?

Rolshan