I asked for information from the Treasury for as far back as 2000 but could only get information back to 2008 on the return on equity of the portfolio of state-owned enterprises to the taxpayer.
Source: New Zealand Treasury – released under Official Information Act.
Apparently, long-term information on the performance of the state-owned enterprise portfolio is not available. Anyone wanting to know the performance of an individual or group of listed companies simply looks at the share price was far back as they want. The prices of individual shares reflect market expectations of future dividends and future price movements, and they go up and down as new information is revealed. The history of a share price indicates the ups and downs of a company in one number far better than any other available indicator.
I also included the adjusted rate of return on equity taking out the two dogs in the portfolio: Solid Energy and KiwiRail.
Source: New Zealand Treasury – released under Official Information Act.
Utopia, you are standing in it! 
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