@DialFrost
From Canonical #2: "*So there are no cut-and-dried rules you can always apply in every situation. The best I can offer is rules of thumb. These will work in nine cases out of ten—and nobody has yet figured out the rules for the tenth case!*"

I disagree. Everything in grammar is the result of a rule, and while we haven't figured out absolutely everything, what we know is closer to 99.9% than to 90%, as the post claims. Especially with perfects, I can't think of anything that isn't governed by a known rule, at least nothing that ELL learners would need to know.