Of course, this passage needs to be taken with a grain of salt: When Norman Mailer visited Belarus and asked to see the KGB files, he (as President) asked the chairman of the KGB if he needed to be careful. The answer: "Absolutely not. Show him everything."
Well, the files could have been laundered by then. Likely by Nov. 23, 1963.
Could have, sure. But this is the problem with the conspiracy mindset. Everything that doesn't fit is fake, altered, etc. Nothing is ever what it seems - at least if what it seems doesn't mesh with the conspiracy theory.
Well sure.
OTOH, I have reasonable doubts that intel agencies anywhere release what would be damaging files, especially in Russia.
A general skepticism is not necessarily selective bias confirmation.