No, it isn't very simple. At all. In my example, motor oil is blended from parts to make motor oil. That's pretty much it. If they import the base stocks, which are not just pulled from the ground......they are refined from crude for Groups I, II, and III, made in a factory via chemical reactions from chemical precursors (often petrol based) for Group IV, and refined largely from vegetable oil for Group V.
Then the additives, too, are made from chemical precursors, and turned into additives in controlled chemical reaction processes in a factory.
Then those components are shipped to the UK, where they are blended. They may pull in some parts from other parts of the world (and they certainly do for some of their products.....in some cases, those components comprise well under 1%, but yet that is a HUGE difference). But most of the "effort" occurs in other parts of the world. They basically just mix it all up at the UK.
But okay, what if the crude for the Groups I, II, and III comes from the US? And the chemical precursors from the other stuff comes from Canada, France, Brazil, and Uzbekistan?
A product may have 10 tiers of suppliers. When I was at Ford, we dealt with Tier 1 suppliers. Maybe we get a PCM from Visteon. Visteon sourced chips and stuff from what we'd call Tier 2's (but they were Tier 1 to Visteon). And so on down the line.
That's why, in my mind, where value is added to the product is the most important step for assigning country of origin.
But hey, regardless, we do both agree on SK!