Is the mintage figure for Melbourne correct, the Renniks catalog has 10 million.
reference https://www.allcoinvalues.com/australian-coins-and-notes/1964-australian-penny-value.html
Seemss like they got their mintage from NGC https://www.ngccoin.com/price-guide/world/australia-penny-km-56-1955-1964-cuid-1045015-duid-1216245 even their values are questionable.