So I am goint to guess that in general you are always working with the current and past year of data.
I think I would create a command to limit the sales data to the last 2 years and then ledt join that to the customer table which you can filter on.
so your command will be something like this
SELECT cus_no, tot_sls_amt, inv_dt, orig_ord_type
FROM oehdrhst_sql
WHERE (inv_dt between DATEADD(yy, DATEDIFF(yy, 0, GETDATE()) - 1, 0) AND DATEADD(dd,-1,DATEADD(yy,0,DATEADD(yy,DATEDIFF(yy,0,getdate())+1,0))))
AND oehdrhst_sql.orig_ord_type<>'C'
that should pull all your records between jan 1 of last year and dec 31 of this year
now add the customer table to this command on the customerid as a left outer join to select all rows from the customer table
then in your select statement in crystal filter the customer list to what you want using the customer table not the command (sales)