WGS84
All components of WGS84 are regularly updated. The "Department of Defense World Geodetic System 1984, Its Definition and Relationships With Local Geodetic Systems" document, initially published in 1984, has been revised in 1997, in 2004 (as three editions of the TR8350.2), and finally in 2014 as the first edition of NGA.STND.0036. The regularly-updated documents provide refined descriptions of the Earth and realizations of the system for higher precision.