Unlike the subtle 1-meter difference between NAD83 and WGS84, the shift from the historic North American Datum of 1927 (NAD27) to NAD83 was massive. The origins of the datums changed entirely (from Meades Ranch, Kansas, to the Earth's center of mass).
The Impact on Property Surveys
Because the Clarke 1866 ellipsoid was fundamentally a different shape than GRS80 (NAD83), coordinate values shifted by tens to hundreds of meters depending on the location in North America. When attempting to re-stake a property line defined by 1960s NAD27 coordinates, surveyors must use highly accurate transformation grids (like NADCON) rather than simple block shifts. Failure to do so has resulted in massive structural encroachment lawsuits.