20 January 2021
Hmmm, there really is a file called Gnash.exe in the folder at https://www.emi.ea.govt.nz/Wholesale/Datasets/_AdditionalInformation/ArchivedDatasets/201310_CentralisedDatasetFinal/CentralisedDataset/HalfHourly but you can't see it using a browser because .exe files are not one of the file types we allow to be surfaced in a browser. FWIW, I can see the .exe file using Azure Storage Explorer to view the EMI datasets storage container.
But all is not lost - see item 2 at https://forum.emi.ea.govt.nz/thread/new-access-arrangements-to-emi-datasets-retirement-of-anonymous-ftp/ for an alternative way to browse and download files from EMI datasets, using Azure Storage Explorer as it happens.
As noted in an earlier post above, the CDS was discontinued in October 2013 and it pre-dates the work of the Market Analytics team. Morgan notes above that BigBag.Gnash contained exactly what he/she was after. Whether or not that included metered grid data prior to Aug 1997, I couldn't say. TBH, I would doubt that it did - if the Authority held such data and we felt we could vouch for its reliability, we would've included it in https://www.emi.ea.govt.nz/Wholesale/Datasets/Metered_data.
I hope this helps.