The big issue with credit systems is that the company can just put you on a shorter flight that costs more to remove liabilities for the lowest possible cost. Depends all how the terms are written for the held amounts. Unless the ticket is held as like for like, ie I booked Melbourne - London, so you get the same class ticket regardless of cost. But more than likely its held as a monetary amount, meaning your value for money is probably down considerably.
I had some overseas holidays booked pre-covid, thankfully with no Australian services involved. The US operators offered full refunds, 125% credits for future use or hold of use for like for like travel when things returned to normal. This was similar for others I know had bookings overseas, unless of course you used an Australian travel agent to book it, which you would be stuffed. Our consumer laws just failed completely during covid.
I think there really should be an investigation into how much value for money customers got for their credits.