It looks like they may be considering two different designs. The elevations on one of those PDFs lists it as 670 feet from the west elevation, versus 659 feet from the west elevation on the other one. The roof design and even the position of the slope are different in both versions.
The 670 foot version also just has "notches" above the garage levels instead of those floors being recessed almost all the way around in the 659 foot version. The roof design of the 659 foot version is more like a diamond pattern, whereas the 670 foot one is a flat slope from one side of the building to the other.
There is also a notch in the 670 foot version about halfway between the roof and the garage levels.
http://www.austintexas.gov/edims/document.cfm?id=340483