I'm creating this thread in hope that @Grunt and @Blossom76 may benefit from it.
People who have been Mormons for a long time tend to have an instinctual understanding of what is doctrine and what is not. But the understanding will, of course, vary a little from person to person, and won't always be correct. In recent years, I have seen the Church moving its curriculum a little closer to focusing on teaching doctrine, with a little less emphasis on principles (see below for definitions).