I would imagine that a company's national/continental headquarters is also responsible for making sure each car is compliant with their respective localities as

I would imagine that a company's national/continental headquarters is also responsible for making sure each car is compliant with their respective localities as part of the process of readying it for sale (especially in the US, where individual states can have their own emissions standards that exceed that of the federal government). Even if VW of America didn't design, build, or request the cheat devices, they're still partially culpable by either unknowingly offering the cars for sale (and not doing their own independent tests in advance of the third-party testing that detected the cheat devices) or knowingly offering cars for sale that didn't meet local emissions standards.