They say that 5.9M people already have a record, but what they neglect to say is that more than 1M of those were the result of the 2016 'opt-out' trials.
Department of Health | Evaluation of the My Health Record Participation Trials
From
https://www.myhealthrecord.gov.au/about/privacy-policy
There are limited other circumstances in which your information may be collected, used and disclosed under the My Health Records Act. These limited circumstances include the provision of indemnity cover for healthcare providers, disclosure to courts and tribunals, for the purposes of coroner's investigations, and for law enforcement purposes.