I don't know. However I presume that when A transfers money to B...

I don't know. However I presume that when A transfers money to B in payment of something very seldom the courts go to the extreme of annulling the transfer, specially when it happened long ago. This because the courts don't want to cause undue disturbances to economic life.

Moreover, in the example given by you the money not only had changed hands but also the transaction could not be reversed.

If illegal under Australian law then the people responsible for the deal should have been charged, but whether that happened or not I cannot remember.

This is my interpretation as a lay man with a very rudimentary knowledge about law as I am not a lawyer.