Only a fraction of NK's artillery is within range - the missiles and 170mm guns, and even then, they can only reach the outskirts.

I read elsewhere on the interwebs (so it's obviously completely true) that the failure rate of NK munitions is 25%.

After all, when the Dear Leader comes round to your factory and asks you whether all your rockets work, do you:

(a) Say "Yes! Thanks to your insightful leadership and guidance, we have completely eliminated errors in our enlightened manufacturing processes!", and then amend the paperwork accordingly, shipping everything in the quota to the army as required, being careful to put your rival (at the other factory)'s name on the dispatch note

(b) Say "No! Our slave-based factories inevitably produce a load of old shite, so we must throw away a quarter of everything we make. Under arrest, you say? Off to the re-education camp, along with my entire family, you say?"