I'll assume that is the case, but that says exactly nothing about artillery capability or the damage this can do in just a matter of hours. How many pieces of (often fortified) artillery do you think those 427 places can take out before shelling starts?

The report you link to provides no evidence that NK has the capability to launch such an attack. The idea that NK has 6000 serviceable artillery tubes and large stocks of serviceable ammunition in the field and ready to be used within an hour is difficult to believable, especially without evidence. This would require propositioned weapons and munitions similar to the Maginot line, which NK does not have nor can it afford.

I'll also point out that ROK and the US maintain 24/7 surveillance of NK depots and munitions storage areas (and pretty much everything else). NK could not attempt to mount such an operation without being detected. Unless they use their 100 year old stealth biplanes, then all bets are off.

> air force

It's just a single branch of military, quite useless if there is modern missile-based air defense in place.