Personally, I'm not at all worried if the Potion book hardly makes an appearance in the film; wasn't HBP more about Harry and Dumbledore finding out how to defeat Voldemort? Sure, it would make sense to put it in, otherwise the people who haven't read the book will be left wondering who the Half-Blood Prince is, but I don't think it's entirely necessary.
However, I wouldn't worry. Just because the book isn't appearing in the trailer (or at least making a prominent appearance; I'm sure it's in there) doesn't mean it won't be in the film. Trailers are supposed to give people the gist of the story, and get them excited for it; shots of books probably won't grab people's attention.
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