That link shows the area that the North American Datum 1983 covers and one thing I note is that it doesn't cover North America. It covers all of Asia and Europe and north Africa but not Europe. Why is this?
This is a rendering error in the spatialreference.org website and a common issue for GIS software.
The stated longitude extent covers from -52 to +172. This should actually be -52 to -180 and +180 to +172 since the datum extent crosses the -180/+180 International Date Line.
You'll also notice the same issue for Russian datums, such as Pulkovo 1942.
(Side note; the International Date Line does not follow the 180 degree meridian exactly.)