Harry Potter and the Prisoner of Azkaban
- The first book describes Marcus Flint as a strong sixth year, but in the third book, two years later, he’s still Captain and Chaser. He had to have finished school a year ago. (Joanne Rowling was asked about this in one of her interviews; she answered: "He stayed for a second year!" Most likely, it was just an excuse.)
- At the beginning of the book, when Harry gets birthday gifts, is says: "Harry sat on the bed, took the package, brought by Arrow, tore the wrapping paper and saw an envelope, a gift in golden foil, and a greeting card. It was the first time Harry got a postcard.” This is nothing to cry about since in the second book he got for Christmas "... the new hand-knitted cardigan and a big cake with raisins from Mrs. Weasley.
Harry Potter and the Half-Blood Prince
- On page 499. Professor Slughorn soothes Harry saying that he has already checked all bottles to make sure there is no poison. He says: "After what happened to your poor friend Rupert ...,” referring to the poisoning of Ron. What does it mean? Perhaps J.K Rowling thought of the actor Rupert Grint at the time of writing this book as it does not seem to be a typo.