Authors can be nice human beings...
But they are not necessarily motivated to help anyone and everyone who contacts them and asks for information.
Did you offer to compensate them in some way? They might appreciate financial compensation. And guess what, you never know if they might decide you've shown good faith, turn down your offer of money, and help you out for free.
Even so, an author is motivated to protect his knowledge which he has gained from his own hard work. He does not want to 'give away the store'.
I would not be surprised if many authors omit one or two key pieces of information, while they explain just enough to support the validity of their treatise.