The Valentino rear derailleur (offered as an option on one model) came 
  out in '64 I believe, so this marks the earliest the catalog could be.
  The Svelto came out in '63.

  The Campy Gran Sport rear derailleur offered on other models might peg
  the upper limit for the year - after the Record R. der. was introduced
  in '63, how much longer did they produce the Gran Sport?  Frank Berto 
  says not at all, the Gran Sport was replaced by the Record in '63.
  (Note to you young'uns, I'm not talking about the 1974+ aluminum 
  Nuovo Gran Sport, but the 50s-style bronze and steel one.)

  According to this Dawes catalog, there must have been at least one year
  in which both Valentino and Gran Sport derailleurs were made - but then
  again, catalogs lie!  For example, note the brakes on the Concorde are 
  listed as Weinmann, but the picture clearly shows Universal 61.  Oops.
  
  We are grateful for any evidence - or even guesses - you'd care to share.

  -Mark Bulgier
  
  To email me, turn the following into a regular email address: 
  mark "at sign" bulgier "dot" net