World Geodetic System 1984 (WGS84) is an absolute positioning system with no ground controls but exclusively based on satellite orbits with no ground controls. It was created by the Department of Defense (DOD) for the satellite systems. As first released in 1987, WGS84 was based on Doppler measurements. In 1994, WGS84 incorporated GPS and also became a dynamic reference frame through its association with ITRF.
The below shows the 4 updates of the WGS84 reference system
release realization/epoch identical to
1987 “Original” WGS1984 NAD83(1986)
1994 WGS84(G730) ITRF91 or 92 - varies in literature
1997 WGS84(G873) ITRF94 or 96 - varies in literature
2002 WGS84(G1150) ITRF00
2012 WGS(1674) ITRF08
* G denotes GPS and week number starting from Jan 2, 1994.
On 8 February 2012, GPS week 1674, NGA implemented the latest realization of the World Geodetic System 1984 (WGS 84), bringing WGS 84 into alignment with the International Terrestrial Reference Frame of 2008 (ITRF08)." The most current realization of WGS84 is WGS84(G1674).
External links to more on evolution of datums : NGS/R. Snay and T. Soler, Electronic Data Solutions