The fact that we worked it out before sending out those satellites is a minor miracle in of itself

Yeah, the idea that you can triangulate from the delay in receiving timestamps that are synchronized within (40ns? seems high, see below) isn't that mind-blowing. If you have synchronized clocks and a mechanism that records timestamps from various locations with those clocks when you get a voltage spike on an antenna, you can triangulate lightning strikes to within several hundred feet - from practically anywhere in the hemisphere (blitzortung.org).

But i like pointing out that it was the relativistic part that was impressive, for sure.

40ns seems high since you can have an "error" after many hours of receiving of less than 10ns, and on a good, clear day, you can get to within 1ns, on cheap hardware. My GPS drift is 10 feet over a week, gradually getting smaller. If i put my good receiver in the center of my kitchen, the points converge to within the confines of the walls within 48 hours.

However this may just be error correction, and the satellite clocks may be inaccurate to 40ns, i am unsure.