I agree. I just mean, you can pretty well know today's state, at least hypothetically. But you better be watching tomorrow's legal news to see if anything important changed.
I'm serious. Pick any non-trivial issues of law, ask a world leading expert, and you'd very quickly hear the word "probably" somewhere. Less often than "it depends", but you'll hear those words often nonetheless.
If that's "knowable" to you, I guess it's knowable.