You think you're being clever but you don't get it: it's NOT POSSIBLE to predict complex system for such long times in advance because they "explode"/diverge way too much so no amount of "validity" or "confidence intervals" help you because you do NOT KNOW HOW MUCH THEY WILL DIVERGE: and THEY WILL.
You can't even predict a double pendulum after a second or two: nature is trillions of double pendulums in a chain: you must be delusional to think you can predict that!