Trade Agreements (to which Invoice Declarations relate) are a topic on their own. One agreement which may be specified on the commercial invoice (in lieu of using a Certificate as proof) for preferential duty purposes is the EU (European Union) Trade Agreement. This agreement was established between the EU and certain countries in the SADC (Southern African Development Community).
The golden rule when third party invoicing is involved in international trade consignments is to “use the last invoice”. Third party invoicing refers to invoices issued by a third party, i.e. a buying or selling agent.