I have at least a casual tag for a lot of what I know, even if it's no better than "I read it somewhere on line"-- at that point, at least I know I haven't checked it farther.

There's another advantage to tagging with "X believes", though more exactly, it should be "I remember X said they believe"-- it can slow down the jump from "X believes thing not in my map" to "X is a fool". This is implied in your point 3 at the end, but I thought it should be made explicit.