Returning to the topic, I ran it past historian Gordon Reid who worked in TN/QF ops and he advises as follows:
28/03/93 there was a timetabled interchange of aircraft between Qantas and Australian so that could be the date we are looking for.
On that day VH-EAM operated TN530/461/42/45 SYD-OOL-SYD-PER-SYD
VH-EAN operated TN8 SYD-PER and VH-TJK operated QF21/22 MEL-SYD-MEL.
In 1992 there were Qantas aircraft operating TN flights but on an ad hoc basis.