I agree that the expectation around outcome for class actions is...

I agree that the expectation around outcome for class actions is a major valuation factor and, given the number of actions, difficult to adequately assess. Regarding the shareholder class action, the link below gives a report that shows the outcome of various shareholder class actions (pages 12 - 15 of the report/pages 14-17 of the .pdf). It may help to indicate the range of outcomes for that particular class action, assuming it is successful.

https://www.chubb.com/content/dam/chubb-sites/chubb-com/au-en/business/large-multinational-businesses-insurance/documents/pdf/chubb-clyde-security-classactions-white-paper-for-apac.pdf

You may also want to apply the odds of the action not being settled - I read elsewhere that around 55% of shareholder class actions settle, whereas the remainder are eventually dismissed. However, presumably the odds of settlement rise the longer the case persists, so would probably need to allow higher odds.