The black backing plate with cable stop guide was original, continuong a ways into the Nuovo Record era, which I will call began in 1968. The top tier changed to chrome plated about 1971ish
Not a model year designation, call it a running change and stocks just got used up.
The subordinate group levers often with the later units had slotted screws... But so did the early units before the ringed screws allowing finger adjustment. When the superleggero black pedals arrived some clients wanted the black plates for aesthetic reasons! 1978 ish brought the dropping of the cable guide. Soon followed by the design simplification of the lever. (Left out the closed C open C transition)