This 1971 Romet booklet is the earliest mention that I have seen of the double cable ZZR (1st style). This derailleur is a copy of the 1951 Simplex Juy-51. This implies that Romet actually introduced a copy of a 1951 design sometime after 1967, and possibly as late as 1971. What can they have been thinking of? Even behind the Iron Curtain, both Kharkov and Favorit had long adopted parallelogram derailleur designs by this date.