GPS constellation and individual satellite status is updated every working day and is also available on the USNO Automated Data Service.
Block I are referred to as the original concept validation satellites developed by Rockwell International and reflect various stages of system development.
The first Block II satellite was launched in February 1989; the most recent Block IIA satellite was launched on September 12, 1996.
Time Service Dept., U.S. Naval Observatory, Washington, DC