The growing conditions that you describe are for parts of the country when you have rainfall in late Spring and Summer and therefore grasses to nurish livestock. However, they call California " the Golden State" because the hills and dales are a golden brown from April through Nov. for lack of rain. When the grasses go dormant and turn brown , their nutrition content drops to next to nil. Therefore, Salatin's studies, books, tours of his farm, etc. apply to his neighborhood , but DO NOT apply in the arid West. A prudent livestock owner wants to have their newborns to be born just as the rainy season starts in late Nov. or Dec. to take advantage of new and nutritous grasses that sprout with the arrival of the rains. Those lambs, calves, etc. that are born in late spring / early summer will be FAR behind their fall /early winter born ones and will have to be fed purchased hay and grain and still not catch up. A waste of time and money. Soar and others in Cal. ( arid West ) should have their ewes drop their lambs in late Nov. / early Dec. and not stress over their lambs being born in Jan. or even later. Practice good husbandry based on the environment that you live in, not on some guru's preachings.By raising the hair breeds you have more flexibility as to when you have your lambs, so why not have them drop when it's warmer out? A good model to follow is to drop lambs when other ruminants in the wild are doing so...the graze is richer, so the milk is more rich for the lambs, one doesn't have to worry about cold weather being a problem, and you have to flush less when the pasture is more nutritious.
Salatin has done studies that show that calves and lambs born later in the year, in the spring months, grow quicker and make more weight gains than those born earlier in the year, so the extra months doesn't really give those early livestock births an edge at market time in the fall. There is also more profit in spring lambing as there are less losses due to the cold and wet found in earlier months.
I never have figured out why farmers want to have lambs and calves when the snow is still flying...it just doesn't make any sense in any way. It's hard on the mothers, on the babies and it's hard on the farmer and it decreases the total profit of it all, so why in the world do they do it?