Average without considering the current selections

[#1]

hello, I am trying to create a document to manage a fleet vehicles.
I have a problem in dealing with the total average of the values on a monthly basis without considering the current selections. Now I managed to make the average dividend for the months numbers and color the cells if the values exceed 40% or 60%, the problem is that not all of the "plate" fields have monthly values so the media is not correct and especially if I change the selections change my media.
I wish the total average of all the years that is the total sum divided by the number of months the single "plate".
I attach an example, and I hope I was clear .
Thank you