www.chrono24.com
This appears original to me. I also came across a wonderful article here www.rescapement.com
s
were they name dial variants for my favorite vacheron reference the 4072. The dial 3 variant is dedicated to black enamel versions where - of the 6 dial variants - the 3rd (black enamel) is indeed the most rare. In there survey of 80+ watches (small in comparison to the known 1178) there were only 2 known. One of them for sale on chrono24.