Originally Posted by evwxxx

Not sure why you would say the 144bcd cranks were only available on a "limited" basis until 1968. The campy timeline at velo-retro.com states:

"1966 - The Record crankset is changed to a 144mm bolt circle (41 tooth minimum chainring) from the previous 151mm bolt circle (44 tooth minimum chainring)."

Then, the NR derailler is announced in the end of year catalogue #15, which would indicate it probably did not become widely available until 1968:

"1967 - Catalog #15 is printed for the year-end trade shows.
Included for the Record group is the Nuovo Record alloy rear derailleur..."

Since the Record rear derailler came out in October 1963 (according to the timeline), there would have been 3 months in 1963, then 64 and 65, where the only available combination was Record RD with 151bcd cranks. Then, in 1966 and 67, the available combination would have been Record RD with 144bcd cranks. Then, from 1968 on the combination would have been NR RD with 144bcd cranks.

So, there would have been 2 years and 3 months where the Record RD/151bcd crank combo would be expected, and about 2 years where the Record RD/144bcd crank combo would be expected. All of this, of course, assumes the timeline is accurate!