In sales and trends, why does proceeds divided by sales only = 66% and not 70%?

Recently Apple started including "sales" in iTunes Connect Sales and Trends which denotes the total revenue your app has made before Apple takes its 30% cut, while "proceeds" is what you made after the cut is subtracted.

Why is it when I take my lifetime proceeds and divide it by my lifetime sales, I only get 66-67% instead of 70%? What is happening to this other 3-4%?