EDX Dispatch - <Supplier Part Id > picking wrong number

Hi,

We are doing an edx dispatch for one of our vendors. From past couple months, when we do an EDX dispatch, the XML show a different number on for the " <Supplier Part Id >"

field rather than whats on the PO_LINE - Supplier Item ID field.

Weirdly, this is not happening for all the POs or the Lines. Its inconsistent.

I wanted to know, where is the code for gnerating the edx XML ? also, which field does the EDX XML picks from ? Is there any other table.field other than the PO_LINE.ItM_ID_VNDR field that i should be checking for ?