Velocity can be as important as money supply in determining economic activity and the aggregate multiplier. If citizens feel constrained to hold their monies it matters less what the state of the money supply is. I also ponder the role of inflation in adding employment to the economy. I don't mean to belittle Okuns law, but the reason it works is the asymmetrical information. The asymmetry involved in finding extra money in your, or your business's bank account. If you knew it was inflation, rather than your business acumen, you wouldn't spend or hire. I guess that is why Okun can't be exploited.