Putting aside the fact that the numbers are year over year and not month to month, that isn't how percentage increases work. If you have a quantity that goes up

Putting aside the fact that the numbers are year over year and not month to month, that isn't how percentage increases work. If you have a quantity that goes up 9% and then goes up another 7%, it has then gone up (1.09 * 1.07) - 1 ~= 16.63%. This is how compounding works. In a single period, it doesn't make much of a difference, as you can see, it's barely more than 16%, but over many periods, compounding results in much greater cumulative growth than if you simply added the increases together.