39mm or 42mm can both be correct. Super Record headsets had a change, early ones had an alloy washer that was the same basic form factor as the steel predecessor. Later units had a taller machined washer with a recessed area and lettering in the recess around the circumference, I have not measured it in a while but I bet it is at least 2 probably 3mm taller than the plain one.
The later washer was also of a larger outside diameter, it helped the wrench stay in place on the upper cup during adjustment.
Obscure Campagnolo fact perhaps, Campagnolo advises to perform the final headset adjustment with the handlebar stem in the bike. A little difficult to do, I used a cut down problem stem's extension as a work around tool, one can always then spin the fork (assuming no brake installed) and follow the procedure. Campagnolo must have felt that the stem installation could possibly alter the adjustment. Perhaps for the gorilla mechanics that tighten the stem to the point of bulging the steerer.
John Jorgensen
Palos Verdes Ca