|It's been a while, but I think there's a comments part on the order form? I didn't realize that until later, and that I could have lumped together different cover sizes to get a cover special if I'd used that. I also didn't really understand the buy 12 get 1 free deal (I think I though that one of the 12 would be free, but in retrospect, I guess I didn't read it carefully). Because of the size of my order I qualified for two, and they put in one of each type of diaper that I'd ordered, OS and S Sandys, so they really do try to give you what they think you'd like. But they're guessing, so tell them if you have a preference.
Although I'm the same way with preferring to do things online, in this case I would call, to make sure you get what you want. ME customer is super nice and helpful.