Supervision of actual braking curves through PZB was actually only introduced starting in the mid-80s (first version of the PZB implemented through microprocess

Supervision of actual braking curves through PZB was actually only introduced starting in the mid-80s (first version of the PZB implemented through microprocessors), and widespread retrofitting of older rolling stock with an upgraded PZB-version only began in the late 1990s/early 2000s in response to the Rüsselsheim rail crash. Before that, speed control only happened at discrete points along the lines of "speed must be lower than x kph after y seconds", so you could actually continue running at full speed for up to y seconds before tripping the train protection. Meanwhile, the currently existing lines on the two pre-war Underground rapid transit systems in Germany (Hamburg and Berlin) are still using simple train stops, too (though they did at some point upgrade to magnetic/inductive train stops instead of the original mechanical train stop system).