run-in [ break-in / running ] period was recommended by manufacturer for approx 1000 kms [ approx 600 miles ] for cars manufactured during 60s'& mid 70s' and the engine piston rings seat-in the cylinder for optimum performance.
afterwards the milling / machining technology changed and lubricants were precisely blended so need of run-in / break-in period has reduced. It is always mentioned in every new car owner's manual.
however driving / using a car with extra care shall always be priority to keep performance at optimum for extended period of time ! cheers !