(That's of course the stuff that makes it into the archive. The British government has also had systematic processes to stop records of their crimes being archived in the first place)
When I read this, I was curious: New Zealand has a statutory process for temporary return of archive material, so does anything similar happen here? I used the OIA to ask Archives New Zealand some questions about temporary returns and missing documents, and the response I think is one that can give us confidence that our history is secure:
The number of items temporarily returned to originating or controlling public offices differs each year based on demand. The Government Loans service processed 3,482 files for offsite loan during the 2017 calendar year. For 2016, a total of 3,408 items were issued; 4,166 items were issued in 2015. These numbers cover all of our offices (Auckland, Wellington, Christchurch and Dunedin).
[...]
We find that our government loans clients take the security of the items they borrow very seriously. There are 22 items listed as ‘Missing – Government Loans’ in our system.
I've asked for a list of those files, but the overall picture appears to be good. You'd expect a small rate of loss as part of the bureaucratic process, but this appears to be extremely small indeed. Unlike the UK, we don't appear to have systematic government destruction of our history. But I guess we have far less to be ashamed of...