Pretty sure that for CGT purposes, ASM shares acquired from the...

Pretty sure that for CGT purposes, ASM shares acquired from the demerger are taken to have been acquired on the date the corresponding ALK shares were purchased. From the ATO class ruling:

Acquisition date of the ASM shares for discount capital gain purposes

16.For the purpose of determining whether you are entitled to make a discount capital gain from a future CGT event that happens to an ASM share you acquired under the demerger, you are taken to have acquired the ASM share on the date you acquired, for CGT purposes, the corresponding Alkane share (table item 2 ofsubsection115-30(1)). This isthe case whether or not you choose demerger roll-over.

https://www.alkane.com.au/wp-content/uploads/2020/08/ALK-ATO-Demerger-Class-Ruling-Aug-2020.pdf