I flew RC missions from 75-80. I can only remember being escorted on a bare handful of them and those were in the Med off Libya. Navy Tomcats were the escorts.
I flew NK missions more times than I can count. Never got intercepted. They tried, but we have ways.

Well, we had ways. I been out of it a long time now. Never intercepted by the Chinese either; we didn't let them get close.
Russians? Sure, NP. Intercepted many times by them. Cubans? Sure, NP. Intercepted many times by them.
And we flew about 20 miles off the coasts, not 150.
Reconaissance isn't considered hostile unless it actually crosses from International Airspace into National Airspace. Those Bears the US escorted down the coast weren't considered hostile, any more than we were when the Russians intercepted us off Vladivostok in International Airspace.
Both sides saw the value of Recon. It's just that there are some countries that are not considered "stable" so you don't give them a chance to prove it. NK is one of those. Well, it was that way when I did the job.
I'm thinking Tac Doctrine must have changed with respect to NK in order for them to have gotten that close. Two other possibilities: Somebody on our side screwed up big time or NK has developed capabilities that they never had before and very, very few folks DO have.... if any one does.
And, like Forrest Gump, "that's all I have to say about that".