William Forster Lloyd in 1833 discussed this problem in the...

William Forster Lloyd in 1833 discussed this problem in the Tragedy of the Commons.
No need to read his book to understand his economic philosophy because we have real-life experiences.
The Craigieburn dumping in Nth Melbourne is another example.

Sorry to inform, Giovanni, again nothing is straight forward with the ATO.

If the sale of shares cannot be identified to specific unmistakable parcels, then the ATO prefers a LIFO (last in first out) valuation for the shares sold. FIFO (first in first out) is not viewed as favourably for some reason. Last I checked, the average cost was acceptable, but that is so fiddly to compute and keep track of if one has many ARL share movements in a year.

I buy and sell my shares (any of them, not just ARL) in specifically identifiable parcels to meet ATO’s requirement. So I will buy in unusual but different numbers on each occasion: 10,010, 20,020, 30,030, 11,111, 22,222, 33,333, etc. You get my drift.
When I sell, I sell in the exact same unusual numbers as bought. That way, I can reasonably prove to the ATO that, yes, the sale of shares can be identified to specific parcels.

Unless you can identify the parcels of shares sold to specific parcels purchased >12 months ago, the ATO will want know how you do the costings on the shares sold and which of them are held for more than and less than 12 months.

You will therefore need a convincing explanation because not a few taxpayers in the past would have tried to pull an easy one on the ATO. And failed.

My suggestion is that you familiarise yourself the tax stuff we discussed here, make notes, and then double check with your tax agent.

Not implying anything about on your tax agent at all.
But I had had to explain to some of my work colleagues’ tax agents how to treat certain technical revenue and expenses items.
Either the tax agents didn’t know about these tax treatments at all, or they got it wrong because the tax treatment can be different in the private vs NGO sector. An example is fringe benefit tax.