Unless I'm woefully off base here, if the satellites were incorrect, you would basically be permanently 300m off, not just temporarily. There's not so many GPS

Unless I'm woefully off base here, if the satellites were incorrect, you would basically be permanently 300m off, not just temporarily. There's not so many GPS satellites out there that you're going to be bouncing around them all the time - even if only one is affected, it would be very noticeable for extended periods of time.