I figured it was a photo artifact until I saw the picture of Peter Cohens watch today which seems to confirm my initial impression. In the follow up message from Boyd is a pic of his LeJour which has a convex case adjacent to the distinct ring like bezel. I have a Pasadena 750.501 (1980) which has the LeJour type of case and bezel. It also has the (day date automatic Pasadena) dial like the 750.50 280SL pictured in your article. Any comments on these variants?
I own Black dialed 5100 and 7750 watches from well over a half a dozen different brands and except for the "Poor Man's Heuers" of Tourneau and Leaderer, they all have slightly different styling in the overall case shape and the area around where the bezel, case and crystal meet.
At some point I plan to get all of my variants on a table for a massive photo session for comparative purposes and to commit them to web pages. Just haven't gotten around to it. (if y'all ever see a round tuit you'll let me know right?)
This is a great story which has inspired me to contact Shane Ede to get my Pasadena fixed up too. Right now it is on a black Bund wrist strap which looks better than the bracelet.
Part of our mission is to encourage people to preserve these great little machines. Sometimes a little photographic persuasion is in order!