Sum without duplicates based on criteria from different cells

I am able to sum the "#of accounts" worked by month on the Summary tab based on the data on the CSO tab. I also need the sum #of accounts worked without duplicates based on the ID#. I have tried multiple ways and can't get it to total correctly.

I would expect B7 on the summary page to be 8 (5+2+1) when the duplicate ID#'s are ignored for that month.

Any suggestions?