Calculated Column with MAX Date

Hi, I have this calculated column called "Ready for Prep":

I need to improve it by making the IF take into account, for each KEY, the MAX date in the column "Change Date".

In the example, I want only a "1" for the first row (which has the MAX date , 04-Jun-2020)

Another way to put this is:

I need to Count the KEYS with the MAX "Change Date" when the column "To" is = "Ready for Development "

Thanks a lot!