For Saatchi in London, 36mm case, concave bezel, modified 5140 dial to fit smaller case, less than 20 made, two backs, deployant buckle, and winding box. Does it get more special than that?
The normal 3940 does not have this issue. If you ask the dealer if the bezel is is convex or concave that will be another clue. Also ask if the case is 36mm or 37mm. The cert says it is a 3940, but if it has the characteristics of the 5140 then it is an anomaly...which in the long run will actually
Suggest you ask seller for a photo of Patek cert to be sure. The 5140 is only 1mm larger and also has a convex bezel instead of the concave bezel of the 3940.
Maltie the image that you are showing as a 3940 is actually a 5140, same movement with a larger case so the dates 5 and 27 are smaller. A beautiful watch indeed and a great choice!