Question: How To Estimate Surviving Population Of Old World Coin?

Hi wizened. The 1925 penny from Australia certainly did not have a mintage of 1,639,000 and they were certainly not melted. In 1925 the mints (Melbourne and Sydney) struck pennies but most would have been struck with dies left over from 1924 (perhaps even older date leftovers as well?). Sydney never received penny dies in 1925 and did have leftover dies. In fact the use of old dies was common as I have both 1924 and 1927 pennies struck with the same obverse die that was leftover from 1920 with the 1924 examples struck in Sydney and the 1927 examples struck in Melbourne after Sydney mint closed and leftover dies were reused by Melbourne.
As for ZAR pennies you have to ask yourself how many were kept by British and Colonial troops as souvenirs after the war was over. Perhaps they might have holed it to mount on a chain or perhaps they kept them pristine. And if you rely on ebay for an indication of how rare they are you might get a false impression because if many thousands were souvenired by Imperial soldiers they would have ended up in Britain and Australia and other empire outposts and not the US; so they may be more common outside the US and perhaps more common on ebay.UK or ebay.au