In June, Fred and George Weasley find out they have scraped "a few O.W.L.s apiece". However, in subsequent books, it is firmly established that O.W.L. results are sent home by owl and are not received until August. See more...
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The entry you are marking as a duplicate is:
|Title||Harry Potter and the Prisoner of Azkaban|
|Original entry||On page 185, it says that all the Ravenclaw Quidditch team players ride Cleansweep Sevens. But on page 188, Wood tells Harry that Cho Chang, who is the Ravenclaw Seeker, rides a Comet Two Sixty. [We're not even told *who* says that all the Ravenclaw players ride Cleansweep Sevens: it's just a random, unnamed Gryffindor. They're either making a generalization (perhaps all the *other* Ravenclaw players ride CS7s) or they're flat out wrong. So it's either not a mistake at all, or it's just a character mistake.]|