Populate Identity column with sequential numbers restarting count on change of key field
So it was suggested that I post the answer I was able to come up with to resolve my issue.  I decided to create a new table to make sure it would work and then save that table as the original table.

SELECT
*, ROW_NUMBER() OVER(PARTITION BY YEAR_,MONTH_,DATE_,SALESREP 
ORDER BY   SALESREP)-1 AS DEL_ID INTO

SALES_INFO_SNAPSHOT_TEMP FROM SALES_INFO_SNAPSHOT_TEST
WHERE DATE_ = '10/31/2018'


This did exactly what I wanted.  A column with sequential numbers beginning with 0 and was inserted with existing data into a new table. The sequential numbers restarted at each change in year_,month_,date_,salesrep.

This allowed me to determine which of four duplicate rows per SalesRep to be deleted.  There were over a thousand rows in all for date_ = '10/31/2018' so I wanted to get this right the first time.
So I was able to determine which row to salvage (the same for each SalesRep) and send a DELETE statement.  It was determined to salvage where ID = '1'.

DELETE FROM SALES_INFO_SNAPSHOT_TEMP WHERE DATE_ = '10/31/2018' AND ID IN ('0','2','3')


Worked like a charm :)