Add Sequential Letters at End of String and Start Over for New Fiscal Week

This formula is working to a point. It adds letters sequentially, but we only need it for additional shipments, not all shipments.

Capture4.PNG

Ideally, the fourth row is an additional shipment for ODW and should read DHL-4(fiscal week)-B. Instead it's showing D.
We need the letters to start at A, for each new fiscal week (the screen shot shows weeks 4 and 5.) Do we need to add something to make it see this is an additional shipment?

Capture5.PNG

The yellow banner at the top of the screen gives details of how to attach a sample Excel file to one of your posts. If you act upon it then you might get answers more quickly.

Pete