In the decade prior to UTC (1972) synchronization between atomic time (cesium seconds) and universal time (earth seconds) was accomplished by the application of 100 millisecond jumps in the atomic time scale. Instead of leap seconds there were "leap one-tenth seconds" (though some jumps were a multiple of 100 ms). You can imagine what a pain this was and understand why using whole integer leap seconds was such a welcome alternative when it was adopted in 1972.
Now remember that the 1960's was a pre-FAX, pre-internet, pre-quartz wristwatch, pre-cell phone age. So how did users find out about changes in time scales? One way was through the HP Journal; a monthly hardcopy technical publication by Hewlett Packard. As you know HP was a major player in the Time & Frequency field from way back and their monthly "Hewlett Packard Journal" was a great technical magazine.
Occasionally in issues from the 60's you would find Universal Time announcements. For example, the following box appeared in the lower left corner of page 6 of the May 1966 HPJ issue devoted to the HP 8504A Vector Voltmeter:
See all of page 6 here.
See the full HP Journal issue here.
See the official TAI UTC time scale record here.
Interestingly the 1966 step in the USNO file differs from the one announced for WWVB.
1965 JUL 1 =JD 2438942.5 TAI-UTC= 3.7401300 S + (MJD - 38761.) X 0.001296 S 1965 SEP 1 =JD 2439004.5 TAI-UTC= 3.8401300 S + (MJD - 38761.) X 0.001296 S 1966 JAN 1 =JD 2439126.5 TAI-UTC= 4.3131700 S + (MJD - 39126.) X 0.002592 S 1968 FEB 1 =JD 2439887.5 TAI-UTC= 4.2131700 S + (MJD - 39126.) X 0.002592 S
(2) Hewlett-Packard Journal Volume 17, Number 9, May 1966, Page 6:
TIME SIGNAL ADJUSTMENT
Time signals broadcast by NBS Standards Radio Station WWVB (60 kHz) will be retarded 200 milliseconds at 0000 hours, Universal Time, on June 1, 1966, according to an announcement from the National Bureau of Standards. The adjustment is in accordance with the policy of maintaining the WWVB pulses, which conform to the atomic-reference second, within 100 milliseconds of time pulses referred to Universal Time.
Not only is the broadcast step 200 ms instead of 100 ms but the date is June rather than January 1966. So for any of you trying to recreate exact time from 40 years ago, beware ;-)