Totally watch unrelated but in the Eighties the then phenomenal cassette deck brand Nakamichi had only one importer for the Benelux and they were located in Rotterdam. As the deck I wanted to buy was expensive at my local dealer I searched for another one and found them in Amsterdam. He imported the decks from Germany and they were over 300 Guilders less expensive. After 3 years or so I wanted to have the heads checked and adjusted so I called the Dutch importer. They asked me for the serial number and after some tapping of keys told me the deck was a non-registered (grey) import and they would not service it. End of story. Now the law has been changed and if the equipment is bought in the EU and the factory guarantee is still valid every dealer has to honour it but often they try to brush you off with fairy tales. So I wonder how this will go with grey imported watches. I have no experience with this.
Edit: it was a Nakamichi 581 and I even bought a (wired) remote control. I remember that TDK had special cassettes with a metal frame and yes, I also bought those.