This is another possible v. plausible argument. Is it possible that GPS doesn't require satellites? I would agree that in a given state of affairs, we could establish that GPS is determined using some other method (a.k.a. Voskhod Globus IMP, but that opens another can of worms). Is it plausible? Well, for starters a clockwork GPS, similar to the aforementioned Russian navigation system, requires some admission that their space program was real, or at least parts of it. Additionally, we would need some level of proof that these devices exist. Yes, you could say that this phony GPS we currently use day in and day out utilizes this clockwork function rather than triangulation from multiple orbiting satellites.
Here's where it gets problematic; first, why do these clockwork devices become unreliable indoors? Second, why does the military have the ability to jam these devices, rendering them either useless or highly degraded (very inaccurate)? Could someone from the society explain what sort of phenomena causes a GPS device to become unreliable indoors or how an external signal of sufficient strength causes the device to become less accurate or not usable?