In VBPA table you will get the PARTNER FUNCTIONS of the SALES DOCUMENT
Goto VBPA table with the VBELN number which is Sales document number , then check the PARVW field for the required Partner function
The Partner functions maintained in the CUSTOMER MASTER are available in KNVP table
There will be difference you can find between these two table if any thing added manually during processing of sales order.
Hope it is clear,