No CGT rollover relief. Shareholders selling in first 12 months...

No CGT rollover relief. Shareholders selling in first 12 months from Demerger date will not be entitled to CGT discount

If someone sells their allotted shares how do you value your shares as in profit / loss for tax purposes.
Ok they will have an opening value but how is it determined.

My take on things are as followed – but please correct me if I am wrong.
Let’s use one of NAB’s points as a reference /starting point.

Cost base of NAB shares will be reduced by value of CYBG distribution

Hypothetically if NAB was valued at $35 before the demerger and now $29 (round figures only)
Does that value CYBG at $6 ( NAB’s assumption)
Now if I had bought NAB at $31.80 and they went up by 10% which comes to roughly $35.
So if CYBG was valued at $6 my profit per share would be 10% - .60c Is that what I am taxed on.

I know CYBG is not going to be valued at $6 (I wish)

So the cheaper I had bought NAB shares the more CGT I pay selling in the first 12 months
Or if I paid top dollar and after the reduced value is way above market value do I get a tax right off by selling.

They cannot be 100% profit, only a small portion – but how much in the question ?