Sovereign Populations

I do know that the Australian sovereign, although could be obtained from the banks, was not generally issued for circulation to the public.
It was mainly used to pay for imports into Australia.
That, as I understand it, explains why sovereigns exhibit less wear than half sovereigns, especially with the earlier dates, and especially so with the Sydney Mint Sovereigns vs. Sydney Mint Half Sovereigns.

In Australia, the Half sovereign was issued to the public for circulation in preference to the Sovereign.

Far more Sovereigns were minted, because more were needed for overseas payments. I never seem to read about Australian Half Sovereigns being recovered from shipwrecks. The Duoro wreck is a case in point.

It is my guess that worn Sovereigns would not be used for overseas trade payments because once they were counted and bagged, you would want to know exactly how much gold there was in a bag. It would have a real pain in the proverbial to re count them with each trade. Best to remove worn coins from the system.

Having said that, they would have suffered much less wear with this mode uf use than the Half Sovereign did in issued circulation.

According to English law (see this pdf) - and presumably remaining unchanged under Australian law - a sovereign was no longer legal tender if it had lost 0.6% of it's original weight. For a half-sovereign, the threshold was 0.8%. That may not sound like much, but a sovereign that lost that much weight through wear alone would be worn down to VG or Fine condition, from a numismatic viewpoint, which is why you very rarely find sovereigns that are worn below that. Banks that detected coins below the threshold weight would return them to the Mint for melting and recoining. They would have kept records of how many coins were destroyed in this fashion, but they would not have noticed or cared about which dates were being tossed back into the furnace.

As sel said, the vast majority of Australian sovereigns, especially from the 20th century, never reached circulation either here or in Britain; they were shipped straight from the colonial mints to the Bank of England vaults and stayed there until Britain dropped the gold standard. What happened to then after that is also a matter of conjecture; I suspect many were shipped off to the US to pay war debts and melted down there. But pretty much all of the uncirculated examples we find on the market today would have come to us via this route.

In short, we have no idea of the actual number of gold coins that officially survived. This is on top of any unofficial melting, turning into jewellery or destruction otherwise that has occurred since. But "1% survival after a century" appears to be a good rule-of-thumb, a very typical estimate for any coinage, gold or not.