The short season at SH is more a function of Mr. Youngscap's desire that every member on every visit is treated to the best conditioning. Or so I've been told.
Since Mullen and Valentine are a bit north and east of me, I cannot say how often winter golf is playable there. But here in OG, we play a ton of winter golf. It really is amazing how just 50 miles away the micro climate is completely different. This last year I played Dec. 29th and again on the 2nd of Jan. Between Jan 1 and March 1 we must've played forty rounds this year. When the days are 45 degrees and the wind is under 15 mph out of the NW, golf is playable. Any lower tempts with wind and it can be a bit much even for a die hard nut job. Cart covers help immensely as do propane heaters for those iffy days.
As an example, The high school golf season opens March 1st. Practice begins and the first meet is not usually scheduled until April. This April most of the early meets had to be re-scheduled. Each one of those days the weather was fine here in OG. But in Scottsbluff and North Platte, it was not.
Hope it helps some what, Ben.