I think there's the important point. Is your key actually natural or is it someone else's surrogate key anyway? Going back to the vehicle identification number: that's already a surrogate key. You just did not assign it yourself.
A VIN is not a surrogate key. A surrogate key must, by definition, have no semantic meaning, and not be composed of parts from multiple domains (among other requirements).
I think there's the important point. Is your key actually natural or is it someone else's surrogate key anyway? Going back to the vehicle identification number: that's already a surrogate key. You just did not assign it yourself.