So, according to Wikipedia:
"On February 6, 1959, 1 trains began to run between 242nd Street and South Ferry all times. Trains began to be branded as Hi-Speed Locals, being as fast as the old express service was with new R21s and R22s on the line.[12][13] During rush hour in the peak direction, alternate trains, those running from 242nd Street, made no stops except 168th Street between Dyckman and 137th Streets in the direction of heavy traffic. The bypassed stations were served by locals originating from Dyckman Street.[14]
"PM rush local/express service was discontinued on February 2, 1959, and morning rush express service was revised on January 8, 1962 to running non stop from 225th to Dyckman Streets and 168th to 137th Streets. This express service was discontinued on May 24, 1976, after which all 1 trains began to make all stops."
I have no idea how the trains skipping all those stoops did not catch up to their leaders. Perhaps there was a longer headway then.