Sum sales for one deal that appears multiple times

[RE]

I have a flat excel table that I'm working off of. The table consists of a snapshot of our sales pipeline that is pulled at the end of each month. I am trying to sum the amount of sales for deals that we won but the issue is that the same deal appears multiple times. For example:

Deal A was won on 5/1/2017 for $500 and it will appear in each data pull starting in May until present. If I write a simple measure that sums the total sales it will aggregate the sales amount from May until the last pull. 

How can I make to where it only counts the sales amount for deals that were won once?

[fhill]

Can you post a sample of your data, or mock-up what the excel data looks like currently?

FOrrest