Teine põhimõte on päritolu määramine tariifiliigituse muutuste põhjal. WTO liikmesriikidel soovitatakse kasutada harmoneeritud süsteemi nomenklatuuri, mille on välja töötanud Maailma Tolliorganisatsioon (WCO, endine Tollikoostöö Nõukogu) nii kaubandusstatistika kogumiseks kui ka tollimaksude kehtestamiseks.
... where it is no longer compatible with the interpretation of one of the nomenclatures referred to in Article 20 (6) ... - at Community level, by reason of amendments to the explanatory notes to the combined nomenclature or by a judgment of the Court of Justice of the European Communities, - at international level, by reason of a classification opinion or an amendment of the explanatory notes to the Nomenclature of the Harmonized Commodity Description and Coding System, adopted by the World Customs Organization established in 1952 under the name 'the Customs Cooperation Council ...
In June 1994 the Customs Cooperation Council decided that with effect from 3 October 1994 it would normally call itself the "World Customs Organisation (WCO)" in English and "Organisation mondiale des douanes (OMD)" in French. It retains its old name in all legal documents. To use its new name in such documents could give rise to legal difficulties.
