In the pre WWII era almost all racing bicycles used side pulls. Mafac started to popularize their various versions of center pulls in the 50's. I am an expert on this having spent far too many years of my youth studying the pictures of my cycling heroes. Sometime around 1966 ( I am no historical expert with dates) Campy introduced their sidepull brakes, which were quite nice at the time. The Campy's were so nice that Mafac had to upgrade their center pulls just to get twerps like me to buy them. VERY few of these upgraded Mafac center pulls made it to the states. Most stateside Mafac brakes were the cheesy "RACER" models. Most everybody started lusting after Campy side pulls after Gimondi and Merckx dominated the Tour De France with them. By the mid 70's even Thevenet was sporting Campy side pulls in an otherwise French gruppo.