No worries, thanks for your help. I probably won't be taking it for several more years anyway, but I'm interested in it anywaySorry, I didn't answer the question. Shoulder pricing starts in late Septmber, not positive of the date. Park Car access for Sleeper Plus is mid-October, varies a bit each year. Off season pricing starts November 1st. Shoulder season prices are less than peak, but not by that much. The off season pricing is significantly less.
Sorry, don't know the Spring dates since I usually travel in the Fall.