I worked at a Peugeot-Nishiki dealership when Shimano introduced inch pitch / skip tooth large cogs in the early 1970s. I occasionally had to explain to customers that the 17T large cog would give them just as easy a bottom gear as SunTour's 34T. Shimano claimed the skip tooth design made for faster shifting, but I never noticed this.
I am not sure when skip tooth got phased out, but it probably coincided with the introduction of modern ramped and shaped cog teeth.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069