I think that is an excellent question which I have wondered about as well.
I found this ---- "The Washington-based Institute for Science and International Security (Isis) estimated last year that North Korea had 10 to 16 nuclear weapons at the end of 2014. It based that conclusion on an analysis of the countrys production of weapons-grade uranium and plutonium recovered from spent nuclear fuel."
I suspect China has supplied all the plutonium North Korea wants.
North Korea will act as China’s proxy. Don’t buy into the Chinese condemnation. Smoke and mirrors is all that is.
I wouldn’t doubt you folks already know this.