Other mistake: In chapter 30 of the American hardcover edition, Harry and Hermione find seats in the topmost row at the Quidditch match, but when Hagrid comes to tell them about Grawp he squeezes his way through the row behind them. If Harry and Hermione are in the topmost row, there cannot be a row behind them. (Corrected in later Editions).
Other mistake: When they are meeting in Hogsmeade to discuss having Harry train them in Defense Against The Dark Arts, Susan Bones asks Harry if it was true he could produce a Patronus Charm. After Harry said yes, everyone is impressed and surprised. However in The Prisoner Of Azkaban, Harry produces a Patronus during the Quidditch match when Malfoy was dressed as a Dementor. This was done in front of the whole school. So everyone at the meeting shouldn't have been surprised.