This may be the earliest advert that I have that shows a picture of the Cyclo Route single cable, pull-chain, derailleur.

(Source gallica.bnf.fr/ Bibliothèque nationale de France)

• Publisher: L'Officiel A.C.M.
• Country: France
• Date: September 1950
• Derailleur brands: Cyclo
• Derailleurs: Cyclo Sport, Cyclo Route