That SSR is on page 8 of the CG book - it refers to USMC AFVs entering at night must remain out of play.
if you look at the charts for the KPA in either scenario - they state either L for Left or R for Right sector or NA meaning it can set up in any non-isoloated area.
KPA Defense Sectors are defined in Section 4 of the Smith's Ridge Rules and Section 3 of the Seoul Rules.
Due to the decision to divide the rules between Smiths Ridge, Seoul, and the CG there may be a little confusion, however, understand that whichever CG you are playing then always have that particular map's rules handy and you should be able to get the answers.
However, if you have more questions let me know and I will try to answer or will get you an answer.