"Are you suggesting that with the pre 1990 system such incidents did not place?"
Of course they did Dick.
I recall a Bathurst race day, the regulator used to install a temporary Tower at Bathurst with its own frequency. One of those crappy weather days. One operator elected to go to orange and Bus to Bathurst rather than face the delays. Shot the approach at orange completely unaware that another aircraft had diverted from Bathurst and was doing the same approach at the same time, except he was still on Bathurst tower frequency. In those days we had flight service, they were unaware of the aircraft from Bathurst as well.