Ole,
Thanks for posting the results of your testing. A few observations based on the results:
The older model does seem to have a slight advantage in circle of illumination. This very well could be the result of the change in the mechanical design. I don't have a pre-WWI angulon in front of me for comparison, but from what I recall the newer models have a bigger front rim that is designed to accept screw in filters (40.5mm). I suspect the dark corners in the images from the 1951 sample may be mechanical vignetting due to this bigger front rim. I have Schneider literature from 1939 and 1961. In the 1939 catalog, they list the coverage of the Angulon series as 80 degrees wide open and up to 105 degrees "stopped down". The 1961 brochure still lists the coverage as 80 degrees wide open, but "only" 98 degrees "stopped down". I wonder if this 7 degree reduction in coverage "stopped down" is due purely to mechanical vignetting.
The 1951 model appears to offer better performance at f8 and definitely has higher contrast in all the test shots. You said your 1939 sample is coated. Are you sure? I didn't think Schneider started coating their lenses until after the war. Does your 1939 sample have the little red triangle that Schneider used to identify lenses that were coated? Perhaps it was retrocoated by someone like Burke and James. They retrocoated a lot of lenses, mostly dagors (including an old 12.5cm f9 Zeiss Dgor from the 1930s that I used to own). Or, perhaps it's a bit of natural oxidation ("bloom") you are observing. Whatever the reason, the test images from the 1951 sample are definitely higher in contrast, which also contributes to them appearing sharper overall than the test images from the 1939 lens.
From the test shots it's difficult for me to decide the actual "usable" coverage of the two lenses. I definitely prefer the more contrasty, sharper look of the 1951 sample. While the 1939 sample does provide a larger circle of illumination, to my eye, the sharper overall look of the 1951 sample give it an edge in "usable" coverage. It's hard to draw sweeping conclusions and generalizations from such a small sample size (one of each) and small, online jpeg images, but your test results are very similar to my own anecdotal experiences with several Angulons over the years - post-WWII samples offer superior contrast and sharpness (I suspect this is largely a function of commercially viable coating techniques, but may also be partially attributable to improved glass types, tighter manufacturing tolerances and more stringent quality control standards). For modest enlargements (2 - 3x), I have always felt that the "usable" coverage of the Angulons top out at about 90 degrees at f32. That's a highly subjective assessment, but in my experience, even though the circle of illuminations is much greater (even for post-WWII Angulons), the image get's REAL soft once you go beyond about 90 degrees.
Kerry