OOP: Hermione not knowing something? (mild spoiler)

[ecaplan_52556]

No: HPFGUIDX 64080


Mild Spoiler ahead
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How is it possible that Hermoine didn't know what the grading system was for the 
O.W.L.s?  (pp 310-311, American Edition):

    excerpt>    "So top grade's O for 'Outstanding'" she was saying, "and then
    excerpt>there's A ?"
    excerpt>    "No, E," George corrected her, "E for 'Exceeds Expectations.'

and then she was still unsure enough to keep questioning the older students about 
other possible grades and unsure enough to be taken in by George's (possible) jest 
about the 'T' grade:

    excerpt>    "And then T," George reminded him.
    excerpt>    "T?" asked Hermione, looking appaled.  "Even lower than a D?
    excerpt>What on earth does that stand for?"
    excerpt>    "'Troll,'" said George promptly.
    excerpt>    Harry laughed again, though he was not sure whether or not
    excerpt>George was joking.