In the very recent past perhaps, not in 1965 for example.
Frank, you are not thinking laterally enough old chap!
How do you think ATC keep track of aircraft even today over the GAFA (those without sat data links or ADSB) ?? Let me see.....radio? HF even?, Airways, Time and speed?
Be real Frank, if they wanted to they could have back then too. Stop using the past as some holy grail of security.
Knowing a schedule, the weather and having a hand held VHF I can sit at home and tell you within 30 seconds what the next a/c to fly past my house will be.
J
