This makes no sense if you want the missiles to work as a deterrent. I'm quite sure North Korea isn't actually planning on going to war (and winning it); they

This makes no sense if you want the missiles to work as a deterrent. I'm quite sure North Korea isn't actually planning on going to war (and winning it); they just want to give the impression that going to war would be too costly for their enemies. Giving the impression that their missiles don't work is counter-productive in this context.