Take a Paws, page-33690

Say one day for eg. Gold is $10,000 and you sell say 10oz coins not at the same time but 1oz at a time, (collectables) and you don't even mention this to your accountant but if you get audited you simply say I bought them years ago for $480 each in the late 1990s would the ATO believe this ?
as collectables bought below $500 are CGT exempt

if you don't have any receipts of purchase but you know what year and month they were bought
would that satisfy authorities if they came knocking?