GPS onboard clock is corrected for relativity due to it's orbit height and speed so it's clock time is approximately correct
But measuring the simultaneity of an event between two different points with a moving clock is a lot trick.
But measuring the simultaneity of an event between two different points with a moving clock is a lot trick.
But they weren't. By my understanding, they were merely using the satellite signals to synchronize the ground clocks in the ground frame, and after that was done, the satellite's were never heard from again.