This is not really true - the Simplex plunger gears shifted far better than the Campagnolo Gran Sport with a quick change with almost no overshifting required. This was in large part due to the sprung upper pivot which kept the upper pulley close to the freewheel. Other plunger type gears did not work as well. The Gran Sport was more robust and easier to fit but shifted very poorly especially if the difference in size between the chainrings was more than a few teeth.
Hilary Stone, Bristol, England
Harvey Sachs wrote:
>
> So, by and large, it seems fair to conclude that the Campy GS, 1951, was
> the first successful parallogram rear derailleur from a firm big enough
> to market it.
>
> And it was one heck of a lot better than the plunger units it competed
> against.