Is the Mercedes SL just a vehicle that ranges from $85k to close to $250k, or does it become a separate model?

This is one of those questions that’s difficult to explain, but at some point you have a vehicle with a high trim level and a vehicle that is a different model. Example: I think we all agree that the Subaru WRX is a separate model from the Impreza. But what about the Focus? I think we all see the Focus RS as a separate model instead of a very high end trim level. And yet, google places the RS as above the Titanium trim hatchback while the ST is a separate model. Most people will tell you a GMC Sierra is just a Chevrolet Silverado trim level with a large appearance package.

So when does a vehicle separate from a trim level to a separate model? Is it power, appearance, pricing, buyers, or just whenever the marketing team says it is? I’m thinking instances such as Audi A, S, and RS models or maybe Mercedes S class variants.