From: Washington D.C.
Does it provide plausible data. Yes.
I agree with this entirely. Since it's not like we're doing actual assessments it isn't super important to get things exactly right. It's enough to just make an educated guess given what's out there. Wikipedia, books, magazine articles, newspaper articles, etc. are great.
In truth, even intelligence services are only making their best guess given the information they have available. Very often their best guesses are highly qualified with long lists of assumptions, which turn out not to be true the next time they make an assessment, sometimes resulting in wild swings in their estimates. No matter what you do, trying to predict the future is fraught with uncertainty. Interestingly, in spite of satellites, aircraft, computer hackers and networks of spies, intelligence services also rely a great deal on opened source material. They might be looking at the same material you are. If someone's willing to talk to a spy they might be just as willing to talk to a newspaper reporter?