Don't give yourself ulcers over this. The reason why it feels so bad, is because it feels like you "lost" something which behaviorally hurts much more than the joy if you gained the same amount. You barely notice when you got something as a bonus but losing out even a little bit feels like a slap in the face.
There's no way of knowing if Alterra is going to do next year; they probably don't even know themselves. So you can't play the timing game, you can only just buy based on the info and offers available at the time.
They've already demonstrated a fixed pricing and operations isn't what they do like Vail's price promises.
For example, at the end of this season, Squaw ran promos and cut the prices of their 2 and 4packs which could make you mad if you paid higher price for that same product in early season, or the more skiers on slopes diluted your pass value. However, you got to remember the benefits of flexibility. So maybe you "lose out" a little from the optimum pricing; but alternatively they flexed operations to means extended seasons and not closing 1week past easter from a schedule determined in October;
As long as you buy into their koolaid that generally they are flexing operations and pricing fairly and matches yourmindset, you should be OK that things flex around and even though sometimes you may lose, remember that other times you gain.