Apologies for the late reply. I only saw this post when tdziemia alerted me to it. I have been concentrating on Validating Exonumia & Coin requests and hadn't look at this part of the forum for a few days.
These are the pages regarding this coin from both Australian printed coin catalogues.
Firstly page 118 from Australian Coins and Banknotes 23rd Edition by Greg Mcdonald

Secondly part of Page 70 from Australian Coin & Banknote Values edition 31 by Rennicks

As you can see both editions list 3 different mintage lines for the 1981 5 cent coin.
A separate line for Canberra (RAM), Llantrisant (RM) and Canadian Mints.
That is why Numista has been set up with 3 mintage lines for the 1981 year for this coin,
This pre-dates my time as referee for Australia and until now no-one has questioned why we have it that way.
Personally I prefer to have the three lines so that members can see how many were actually minted at each mint.
I understand that the coins for Canberra and Llantrisant are not able to be separated by examining them and they are identical for all intents and purposes.
I am not going to die in a ditch over it though and if someone is fretting over the fact we show 2 lines for basically the same coin I can join them together. But we will lose that information regarding how many were minted at each mint on the mintage line. I know that I can add something in the comments box about it and I will do that. But it won't be as apparent to members unless they check the comments.
Take care and stay safe. Regards Mike
Master Referee - See my profile for what I collect.