I suspect a lot of important personnel in NK (including some programmers and some university students; that set probably overlaps a lot) have access to the internet, or at least most of it, even if monitored. So don't assume that they're not learning in isolation. But even if so, there are common principles you could study from books and test systems. (They'd be smart to apply their people to securing their own systems as well with red/blue teams...) Plus if you know your target, you can dedicate your time to finding ways to attack that target, you don't need to keep up to date with the latest from e.g. tech talks.