Others l give will give you better stats. But based upon past behavior i would look at this map as a wish list. This is the direction Tesla is headed and is planning to achieve, however, I would be surprised if they achieve 50% of the unbuilt sites that appear on this map. There are still dozens of sites on the 2015 map that will not even be started by the end of this year.
The specific locations shown on the map aren't very trustworthy but over the past two years Tesla has rather consistently built about 100 U.S. Superchargers per year. I would expect that rate to continue, just not exactly where planned.
Treat as "current ambition". Anyone who _depends_ on a certain location being open had best wait until it's actually open before buying the car. Tesla _is_ currently adding at a rate of over 100 per year, so it's not as if they're not working it, but progress depends on locating sites and getting everything worked out, so sometimes they are changing priorities.
According to Tesla's map, Maine should have had 2 Superchargers in _2014_, then another in 2015. It changed to 3 in 2015. And there's no sign of anything.