I think we have had a great times around the 1990's, early 2000's, maybe even 2010's, when we are got our hands many earlier widely not available documents. I remember MiG-29 manuals, T-72 manuals, maybe even F-15 and F-16 manuals and so on.
But those are different times, not just the Russians but even European and US firms provide relatively accurate data about their systems in the military expo's marketing brochures...
Around middle in the 2010's this time become more and more avid, and now became the new "the less we say the better for everyone" age...
So if you believe there is a lurking Su-35S manual somewhere an ordinary military fan SSD, then probably you are not aware of the change of times...