Running Average With Replacement

In the attached spreadsheet, I want to do a running average of the "To" column (column G) for each company throughout the 8 year period. The only problem is I want to do it with replacement based on column D, meaning if the same brokerage firm comes out with a new announcement, it will replace the value of the old one in the running average calculation.

Here is an illustration of what I mean:

Looking at Company A between row 2 and 12, the value for Consensus in row 2 should be the average of Column G in row 2, row 3 is the average of Column G in row 3...row 11 is the average of Column G in row 2 to row 11, but row 12 will be the average of Column G in row 2 to 12 be excluding column 5's value because both column 5 and 12 are issued by the same brokerage.

I want excel to replace new recommendations by brokerages over the old ones in the running average calculation.