Let’s take the Rhine Which goes from Switzerland to Netherlands. When and how did people start agreeing on giving-it the same name ? What about the alps going from southern France to Austria ? When did people agreed that it was the same mountain range ? And obviously what about the Gulf of Mexico ?
Lookup the East Sea, aka Sea of Japan. Or the Tagus river, aka Tejo river. There’s plenty other examples I can’t remember now. People don’t always agree on what to call things that cross borders. Usually we just agree to disagree as there’s no point arguing.