>> terrestrial reference point(s) to correct for orbital drift
> No it does not.
OP's assumption is more accurate than your response. What is interesting is you go ahead and explain how the system compensates for drift, after saying it doesn't. Ground based stations correct the satellite's internal position, the satellite then sends that to the receivers. so where those ground based control systems are located is going to be the GPS reference. 2 SOPS contacts each GPS satellite regularly with a navigational update using dedicated or shared (AFSCN) ground antennas"
Then you missed the second place where it happens, maps are in X/Y coordinates, GPS is in lat/long. So a second ground reference point is chosen, and the GPS receiver decides which region it is in to decide which reference point it will use, then converts the GPS position to a local reference.