In shared shipments, can a seller with an export licence export himself?

Preferably not. While it is technically possible to have multiple exporters in the same container, more than one exporter makes the logistics more complicated, prone to errors and therefore increase risks of delays.

Why? Because each exporter has to produce a set of shipping documents (Bill of Lading, Origin Certificate, Phythosanitary certificate, Invoices among other official documents depending on the origin.). These documents must be checked and sent on time for the container to be imported. If one of the exporter does not comply perfectly, the entire shipment is delayed.