PLovett, are you sure that clinic runs were conducted by RFDS under their AOC as far as I am aware both WA RFDS and Central(NT/SA and WA) only have an aerial work AOC.
Last I heard clinic runs were considered by CASA to be charter not Aerial work. This is why RFDS in WA and NT contract the clinic runs out. If they are doing clinic runs in RFDS aircraft then they must have special exemption from CASA to allow these operations or they have upgraded to a Charter AOC. However a quick search on CASA AOC search shows both WA and Central still only hold a Aerial Work AOC.
Must be a simple explanation.