Origin is a legal construct, not a physical property. Rules of origin determine when processing in a country is sufficient to confer that country’s origin, and the thresholds differ between trade agreements.
Where a restriction attaches to origin rather than to a party, the certificate becomes the control. Cargo blending, minimal processing in a third country, and simple falsification of the certificate all attack the same point, and detection relies on whether the claimed processing country has the production capacity the volumes imply.