^Well, it's not really "messing up," since there's no reason not to put the book on sale early if a store gets it early. Except for really big events like Harry Potter and such, there is no real release date for a print book, just a general range wherein it becomes available.
Exactly. Except for super high-profile events like Harry Potter (or the occasional movie novelization), there are no coordinated release dates for books the way there are for movies or record albums. The books go on the shelves when somebody gets around to cracking open the boxes the delivery guys dropped off.
Glad you liked the book, Fremen! I'll be curious to hear what people think.