I'm terrible at facial expressions, so the entire notion of reading them fails big time with me. Or, as a more appropriate expression "it falls flat on it's face".
But as you mention, the really obvious ones, those aren't hard to miss I guess. Someone dropping the jaw seems pretty obvious, but then again, I think it has to do with the fact that such an expression is a significant expression, rather than a subtle change in eyes, mouth or other parts in the face.
What's interesting though, is that I'm so bad at facial expressions that I'm even terrible at expressing them. I've had sessions with therapists and I threw them off cause my face gave them a different expression as to how I was feeling. So that's an extra issue that comes with it. Not only do I fail in reading them, people fail in reading me as well (and those are the NT's I'm talking about).
As for the type of expressions; I don't think there's a list to see which ones you can and can't read. From my understanding, especially with tests, they come down to facial expressions on pictures and you have to put the correct emotion with said picture. If you're unable to do so pretty consistently (there's a test where you only see a set of eyes and they express something; think it's 36 pictures, and from what I'm reading about it, scoring between 22 and 30 is normal below 22 is the cut off that you're not so good at reading emotions; I remember scoring 4 out of 36 at one time).
The test can be checked out here, but as with any online test, even though it has been conducted by professionals, online tests are to be taken with a grain of salt.
http://well.blogs.nytimes.com/2013/...d-behind-the-eyes/?_php=true&_type=blogs&_r=0