It's trivial to get around these rules. Northern Irelnd is (or was at some point) a country of origin for both the EU and the UK. So a company could produce something in Greece, ship it to Dublin within the EU, then truck it to Belfast in Northern Ireland, and export it to the US with a UK certificate of origin.

Pretty much every single Aliexpress purchase I've made has been shipped from the Netherlands for years now.

They use it to get around EU customs and tariffs, dunno how but it works.