Dealers probably know. One of the big rules in sales though is to sell off of current promos. Even if you know the upcoming promos absolutely do not mention them to the customer. I told people all the time stuff like "we have no idea what it'll be next week/month whatever" even if I knew full well what the upcoming promos were. It makes it so that nobody would ever buy anything because they'd be constantly waiting for a better deal. Granted, I wasn't in car sales specifically, but it's all basically the same.