A census trick question

I was asked on the Ref desk today if we had fiche records of the collectors books from early 20th century census in Australia - say, around 1915.
I discovered there was a census in 1911, but none of the usual suspects (Mitchell Library, etc.) has any primary documents from it.
Then the penny dropped - as the State Library of QLD says in its helpful guide -

Prior to 2001 it was Australian federal government policy to destroy all name-identified census returns for privacy reasons, and all returns for censuses conducted between 1901 and 2001 have been destroyed.

Of course, I should have realised this - there was a question from the 2006 census giving you the option to not have your census questionnaire destroyed, reflecting the new laws post-2001.
Just thought I'd share this for those who may not have realised the situation.
And kudos to State Library of QLD - NSW Archives and Mitchell do not make this information readily available in their guides. Perhaps they assume we all know.
Brian