Google Sheets conditional formatting dates within 90 days

Okay, it is not a very elegant solution, and I know some experts would have a much better solution, but I think it does what you want.
See my tab "Iteration 2-GK" in your new sheet.

You can change the dates in column I to see if the Summaries colours change the way you expect. I haven't done Technical or Stakeholders yet, but they would be the same.

I came up with a complex formula to apply the same logic used in the conditional formatting rules for Column I, to apply conditional formatting for column C. Note that I added a hidden column B, to add the ProductName onto each row. I also removed the merged cells in columns A-E. The formula to check whether the dates in column I fall in a certain range, and then to count which range occurs most frequently (ie. also the most frequent colour in column I for each product) is:

I haven't got this to work, so it needs to be dragged down column C from cell C3.

Will you need to add rows for a product, if you come up with more documentation? I haven't tested yet if this will work when adding rows.