It's frustrating in VCE, but this occurs even more so in uni given that there's often no clear cut study design and they can pull large questions on something very minor. Difference is, hopefully by uni you're in a course you actually want to learn that you don't care whether it's being assessed or not; you just learn something for the sake of learning more about something you enjoy. But for VCE, I find that most subjects will tend to be largely conceptual and that textbooks just write varying amounts or depth into these concepts, often providing plenty of irrelevant examples to illustrate such concepts. These examples are typically not needed, and in general, I'd say that the depth you need to go into is the least depth that is displayed in any of the major prescribed textbooks. This isn't foolproof as shown by the controversy a few years ago over the HHD exam where the main textbook only had 2 sentences on a major short answer question, but I haven't heard of any other major problems with this vagueness. In general, VCAA asks pretty fair questions from what I've seen so don't stress too much. Doing past papers will also give you a feel of what VCAA is likely to ask as well.