Index Match (multiple criteria) Skipping Duplicates & Returning Only Unique Values

Hi, I have been desperately trying to figure this one out. I have assigned a unique value to a set of numbers. I am trying to return the unique value based on two criteria (Dollar amount & Period). The problem i am have is that there could be more that one occurrence where the dollar amount and the period are the same. When this is the case the unique value comes back the same (the first occurrence). I need the formula to skip if the unique value that has already been used and return the next based on the same criteria. I have attached my document. Very simple spreadsheet and very intuitive. Thanks