Match across databases

I have several different Navision Companies with different staff entering data

Boss wants report he can run to show if same invoice has been paid by more than one of them

Issue - Vendor Codes are different , Addresses are not identical ( formats) same with phone Names not identical ( spaces caps abbreviations etc)

this leaves me zip (Postal) Code and external document number( and this one is iffy) or the dollar amount to work with in making comparison

Postal code isnt the issue its the other two

Formula
cell1 NL("Filter", "Vendor Ledger Entry", "Amount", "Company=",1)
cell2 NL("Filter", "Vendor Ledger Entry", "Amount", "Company=",2)
Cell3 NP("Intersect",Cell1,Cell2) I get back 0 no matter if amount or External Doc used in filter

I suspect there may be issue in that amount is a numeric field but External Doc gives same results

Now the real kicker is I don't know if the condition the report is supposed to generate ( Same vendor same invoice paid in more than one company exists in the data but the odds are it has happened at least once)

Anybody have a bettter idea how to go about this ?

Thanks

Van