When is Hermione Granger's birthday? First proper answer 10 points?

according to www.mugglenet.com, hermione's birthday appeared in www.jkrowling.com. it's september 19. i think it's in 1979 because when she turned 11, the term already began so she had to attend hogwarts the following year, same year as harry and ron, when she is about to turn 12. also, her trace was the first to break. she can already do magic outside school in hp7, meaning she's come of age before harry turned 17, otherwise, she couldn't because it was only july.