In the world of collectible vintage pocket knives counterfeits began popping up 50 years ago at the knife shows. Names like Remington (the bullet shield models) Case, Winchester, Russell, and probably a few other HIGH DOLLAR knives. I haven't seen it in vintage razors, though I suppose it is possible.

Maybe Wade & Butcher FBUs would be a likely candidate, since the larger examples bring a good buck. I find it unlikely that anyone would go to the trouble of counterfeiting an obscure British maker using a razor that is in a condition which wouldn't bring much whether it was genuine or not. YMMV.