In New Zealand at least, a lot of this data seems to come from imagery; it's quite outdated, the cables are all missing and the voltages are pretty hit and miss. Cool project though.
The public source of this data (ArcGIS Feature Server account of Transpower) shows data last modified by Transpower in October 2025 for pylons and February 2025 for substations. At the rate of development of NZ, you wouldn't expect major changes to any of this data unless it's a major transmission upgrade project identified years in advance in hundreds of public announcements and documents.
