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 ?
Consider the Thames river. Which one? Depends on how you read it out loud.
The “Temz” runs through London while the “Thayms” runs through somewhere in Connecticut.