Naively, I'd expect that it's where the VPN service is incorporated that determines that stuff. But on the other hand, they would need to find a server to impound it. So I suppose that PoPs could be used strategically to impede investigations.
I dont have adversarial experience with law enforcement, but from what Ive seen it's normally around incorporation, assets, and where the principals are. The government gets access by serving you papers, restricting your assets, or restricting your freedoms.
That side the physical location of the servers will matter for teh same reasons. Two adjacent countries may have different standards of evidence, due process, compelled information, data retention, 'know your customer', etc. Both the country of physical location and the country of incorporation will effectively have access; one directly and one via compulsion.
I was thinking more along the lines of law enforcement as well. Where civil & criminal law, data retention, LEO access, and due process may vary significantly in different countries.