Corrected entry: In Flight of the Fat Lady [Chapter 8] When Lupin says: It would assume the shape of Lord Voldemort. referring to the dementor, the book explains Harry is taken aback, because it is the first time that anyone other than Dumbledore has said the name to Harry. However in Sorcerer/Philosopher's Stone Hagrid, albeit reluctantly, says his name.
Corrected entry: In Harry Potter and the Philosopher's Stone, Marcus Flint is described as a "troll-like 6th year". Yet in the Prisoner of Azkaban, Flint is still captain of the Slytherin Quidditch team. There are only 7 years in Hogwarts and there is no mention of Flint being held back a year or anything else which would explain why he is present in what would be his 8th year at Hogwarts.
Corrected entry: In the beginning of the book when Harry found the Knight Bus, Stan Shunpike is telling Harry what he can do for a certain amount of Sickles, like 11 to get to London. Harry chose one and it said that he handed Stan gold, which would be Galleons, not silver Sickles.
Correction: So? Stan is quoting their prices to Harry, Harry pays with a large denomination and Stan gives him change back.
Corrected entry: After Harry and Hermione return from saving Buckbeak and Sirius, Dumbledore had locked them in the hospital wing. However, it says that Harry and Hermione slipped back into the dormitory, whereas it should be the hospital wing.
Correction: A dormitory is "a room containing a number of beds", like the hospital wing. So in fact, JKR is not referring to the Gryffindor dormitory when she writes this - she does mean the hospital wing.
Corrected entry: In the chapter titled Hermione's Secret, Dumbledore says, "Miss Granger, you know the law you know what is at stake. ... You must not be seen." when instructing Harry and Hermione to use the time turner to go back and save Sirius. Throughout the chapter, Hermione tells Harry that they must not be seen and that he can't interfere for it is against wizarding law. However, during the entire school year Hermione has been using the same time-turner and has been going back in time to complete classes so every time she uses it she obviously has been seen by everyone in her class (as pointed out by Ron. He brings up Hermione's mysterious ability to attend two classes at once, saying "And Ernie McMillan told me she's never missed a Muggle Studies class, but half of them are at the same time as Divination, and she's never missed one of them either!"). Since she is allowing herself to be seen in those cases, why can they not allow themselves to be seen to change the p.
Correction: Nobody (except for some of the teachers) knows that Hermione is using a Time-Turner, but that's beside the point. She wasn't doing anything differently when using it for her extra classes. An example of that would be if she used the Time-Turner to go back to a class that she already did to try to improve on an assignment. If she did that, then there would be two Hermiones in that classroom at the same time, wherein lies the reason that she needs to be careful when using it.
Corrected 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.
Correction: 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.
Corrected entry: In chapter 19, it says that Voldemort was in hiding for 15 years. If he only lost his powers 12 years ago, why would he have been hiding for the extra 3 years?
Correction: Because he was the most wanted wizard in the world, guilty of several crimes.
Correction: This statement is showing that Harry is taken aback as someone is saying it in a casual conversation, not as an answer to a direct question. Hagrid had no choice but to tell Harry since he could not spell the name.