how to find proforma invoice for commercial invoice

Dear sd experts

i know how to check pro-farma invoice

in se16n---give the table VBFA and sub document cat U IT means profarma invoice

but what my doubt is i have created some invoices and proforma invoices  so i want to check proforma invoice  of commercial invoice

and i have checked this link

http://scn.sap.com/thread/1567927

but in se16n at precceding document i cant maintain U