Are there concrete answers to the harry potter series after Voldemort dies?

On various Harry potter information sites, It mentions Harry Potter becoming head auror, and Proffesor Mcgonagle being HeadMistress. Neville longbottom marrying Hannah Abott. However, I search and search, I've reread the books over and over looking for clues I may have missed.Are there other books besides the 7 harry potter books that I am not aware of? I know the epilouge on the deathly hallows mentions Neville being a professor, and Ron and hermione getting married and Harry and ginny and such, but where are the site getting their information? Is it merely a guess?