There are some very detailed, well thought out, and researched answers on this site. However, many answers are conjecture. That is not usually the fault of the person answering the question, due to the lack of information available.
In a perfect world, there would always be some way to authoritatively answer any valid question. This is just simply not possible since many of these authors are long dead, and there is no other source. Think about how many questions would have amazing answers of Tolkien, Heinlein, etc. were still living.
Getting back to reality, there are still some living authors that could lend a hand such as G.R.R.M., and J.K. Rowling, and many others. But, I am not aware of any answers that they have posted themselves.
I have only been able to find one question which was answered by an authority on the subject. The question below was answered by Danny Rubin, who was the screenwriter for Groundhog Day. Are there other questions on the site which were answered by the writer or other authority?