Nice to see you back, Nick!
On the matter of historical precedents for the notch/step lapel dinner jacket, one interesting example I found in the volume for the 1920s in the series All-American Ads published by Taschen Books some years back. On pages 2-3 there is a spread from a 1927 ad for Chesterfield cigarettes. In it, a smiling young lady is lighting the cigarettes of two young men, both in black tie. One is wearing a notch-lapel jacket, the other a peak lapel, so obviously the artist was aware of the difference, and the notch lapel was seeing at least some use during the sartorial "Golden Age" of the interwar years.