Fully operational in 93, but IMO the real slam dunk was disabling of Selective Availability in 2000, which made GPS significantly more useful. WAAS has been amazing for aviation, allowing for RNAV instrument precision approaches to airports with no RF equipment installation required onsite. And there are still innovations getting rolled out, including L2C, L5 and more!
IMO the secret sauce wasn't necessarily the precision but the ability, granted by technology outside the GPS system, to put a dot on a digital map versus your PLGR giving you a pair of coordinates that you had to look up on a paper map.
https://www.gps.gov/systems/gps/modernization/civilsignals/