ASM Chart Thread, page-2236

My understanding is that ASM shares acquired from the demerger are taken to have been acquired on the date the corresponding ALK shares were purchased. The document detailing the ATO ruling on the demerger is on the ALK website. Here's the relevant section:

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 of subsection 115-30(1)). This is the case whether or not you choose demerger roll-over.

https://www.alkane.com.au/investors/demerger/

Disclaimer: I am not an accountant, however I will be visiting one in the near future.

Edit: this was meant to be a reply to Rothbard.