I should clarify, as we're already past the point of getting too deep in the weeds.
The 629K is based off of two sources of data. 1) The AT centerline .gpx file (no elevation data) and 2) the USGS small scale DEM data (applied to the .gpx file).
No GPS receiver elevation data (as GPS receivers are prone to losing signal) was used in obtaining this number, only USGS DEM data.