The 2016 NWCF will be Sept 9-11. I'm not sure how exact the state park website is in regards to dates available for reservation, but basically 9 months ahead, and that would be the begining of Dec.
On the first day of the weekend (for those looking to camp Fri-Sat) they can book those 2 nights when the Friday night is avalable for booking. I'll be bookng the exended stay again, so when Thursday comes available, I'll be bookng through Sunday night.