I've only seen the octagonal Santos with a white dial with Romans. However the dial on that watch is beautiful. I don't know anything of that watches significance. However, the few times I've seen Cartiers with a red cabochon on the crown usually they were a special edition or limited edition of some sort. Have you actually seen papers indicating that it was serviced at a Cartier Service Center and not simply at a Dealer or an independent watch repair shop? Perhaps others can share more about this watch.
Best regards,
Dino