The Australian Taxation Office does have data about superannuation status of Australia-based superannuation funds, but would have limited data about foreign-based superannuation schemes that some Australian residents might belong to, as a result of previous employment overseas. To obtain income data about all those who had a particular type of superannuation, e.g. a self-managed superannuation fund, would require an extensive and probably error-prone data matching exercise. It would be easier and cheaper to collect the data through the Census.
In addition, if data about the total income of retired Commonwealth public servants were available, it would be possible to obtain a better estimate of the likely cost of providing better indexation of their pensions (currently indexed by the CPI). Recently, the head of the Commonwealth Superannuation Corporation, Peter Carigy-Ryan, admitted that that it was "virtually impossible to assess Commonwealth defined benefit pensioners' income". No doubt other superannuation schemes would like to know more about their customers.