Ann: Sale of Shares by Directors to Institutional Investors, page-159

@bz847

You could be correct:

Where shares are sold on-market within 30 days of the deferred taxing point, the taxing point will be moved to the date of sale, and the sale proceeds from the shares can be taken as their market value.

For shares that are not sold within 30 days of the deferred taxing point, their market value is the weighted average closing price for the five trading days before, but not including, the date of the deferred taxing point. It is also reasonable to calculate the 'weighted average closing price' using the closing market prices over the five trading days up to and including the particular day.

https://www.ato.gov.au/General/Employee-share-schemes/In-detail/Market-value/ESS---Market-value-of-listed-shares-and-stapled-securities/?page=1#Valuation_methods