In order to obtain preferential customs treatment, a proof of origin is not enough. The direct transport rule and the principal of territoriality also need to be fulfilled.
As a rule, if the goods have been cleared for free circulation in a 3rd country en route, you will not obtain preferential treatment for your goods when they arrive in the importing country. Some of the free trade agreements have schemes that still allow this to happen.
The main rule is that the goods must be sent directly from Norway to the importing country. However, there are exceptions and the individual free trade agreements includes rules for these.
The goods can be sent via other countries, providing that they have remained under the supervision of Customs Authorities in the country of transit or storage. Originating goods can also be sent to third countries for exhibitions or demonstrations without losing their status as originating products.
In addition to fulfilment of the direct transport rule, the principle of territoriality must also be fulfilled. There is a territorial requirement in most free trade agreements. This essentially means that the originating product loses its entitlement to preferential treatment if the product is outside the scope of the agreement.