And if you look at the map, include future and under construction, you can take that as 100% NZ coverage
"Future" and "under construction" isn't much good for next week's trip or even next year's trip around the South Island! Other than massively expensive Teslas, the only EV that's any good for getting you from Hokitika to Wanaka is a BMW i3 with a range extender, so petrol still has a large part to play for a long time yet!
Until EV supplies exist in numbers, its not relevant. They aren't there to buy. So while numbers are low in terms of current sales of new EV's and probably lower for imported pre owned, people with range needs that aren't met by the network, won't buy. Sales are not affected as others will buy what is a very small number. Long time yet? How long is that? 2 years, 5 years, 10 years? The limiting factor is supplies of cars. That will take a lot longer than a small number of under construction and future stations.
You say that people with range needs that aren't met by the network won't buy. But, you can't always determine in advance what your "range needs" are going to be! At present, it's impractical for most people to just own an EV for all their driving needs. So that's why many EV owners also own a petrol vehicle and I think that situation will exist for a long time to come!