Tom,
Some of the differences between the 1st generation NR brakes and the subsequent ones:
--unstamped caliper arms, as you know --a more slender and flat cross-section on the arms --a big chamfered washer on the front brake stamped "brev camp"--which caused some problems with clearing the headset --the lack of the serrated "rondella dentata" washers (not until 1971) --shorter, more curvy brake levers (sometimes polished, sometimes satin) --slightly different shaped wheel guides --"Campagnolo Brev" on the QR washer instead of "Brev Camp" --I think more reach, especially on the rear brake (but I'm not sure)
More studying will reveal lots more differences, I think
Jack "saw 2 prs of these this weekend!" Bissell Tucson
p.s. just ask if you want jpegs of the different levers side-by-side