Buying a Rolex from some guy in a car park is different to buying one from a jewelers. The former wouldn't protect you in any way, the later would let you demonstrate a good faith belief that it wasn't stolen, and wasn't fake.
This is a tangent but there's nothing wrong with buying a fake. So you can have a good faith belief that it was a counterfeit, which can protect you somewhat in the case that it was stolen.
More generally, say if wanted consumer protections consistent with it being a Rolex, or if you wanted to sell it as a Rolex. Then whether you bought it as a fake does matter.
