An example of the difficulty of determining the origins of products/produce is well known in the oil importing business.

Treaties with Mexico permit Mexican crude oil to be imported into the US at favorible tariffs when compared to the "import taxes" on oil from elsewhere.

Crude oil is brought into Mexico in tankers and transferred to trucks that drive across the border into Texas on a "closed loop road" that connects to NO OTHER ROUTES and returns to ONLY Mexico.

Trans-shipment of oil through the US for shipment elsewhere is untaxed.

By being passed through the US (for free) and imported only into Mexico the oil becomes "Mexican Crude" which is then trucked across the border at "Mexican rates" for refining in Texas and sale in the US.

How do you know where it came from when you pump it into your tank ... ... ??

The description of implementation of the "loop" road is somewhat simplified, but you get the idea, I hope. Similar gimmicks, some less obvious, certainly exist for all sorts of "stuff," some of which we eat and others we only use to annoy those around us by blaring bad music where they can't avoid it.

John