That is certainly the case for Capital gains. I.e. you can...

That is certainly the case for Capital gains. I.e. you can provided you can substantiate it. Cannot believe ATO would have one rule for capital gains and another for franking credits.

Check this link:

https://www.ato.gov.au/General/Capital-gains-tax/Shares,-units-and-similar-investments/Identifying-when-shares-or-units-are-acquired/

And this para

If you have the relevant records from your CHESS External Link holding statement or your issuer sponsored statement you'll be able to nominate which shares you have sold. Alternatively, you can use a 'first in, first out' basis where you treat the first shares or units you bought as being the first you disposed of.