merge duplicate lines while appending unique data

Hello all,
I have an excel grid with thousands of rows and 21 columns of data. Most of the rows have duplicate data, and I want to remove the dupes. The problem I have is:
1. the last 6 columns have unique data, and
2. I need to keep that data.

Is there a way to merge the lines and append unique data after the 21 base columns?

I have attached an excel grid which details what I am trying to do. There are 2 tabs describing what I have now (Before) and what I am trying to achieve (After). I am using Excel 2007.

Any assistance would be greatly appreciated. Thanks!