Property boundaries aren't delimited by GPS coordinates, but rather a surveyor's instructions on how to locate the boundary from a set of known landmarks. In most US states, the Public Land Survey System [1] gives "meridians" and "baselines" for each region serving as the regional center. Radiating out, every 6 miles, is a new "township," with its corners serving as the local landmark for property boundaries.

[1] https://en.wikipedia.org/wiki/Public_Land_Survey_System

But so that means that you could lose land or gain land if enough earth moves and the relative change to the land marks is in your favor or not. But it's just not a big enough of a deal to do it a different way. I do wonder what the most significant occurrence of that is though.

The most significant occurrence is probably land loss due to tidal erosion and/or flooding.

Surveyors reference monuments on the ground. Since tectonic plates tend to move together then so so short lines and their corners.

It can get complicated on large tracts or lengths, but stuff like rail roads and freeways are composed of many small properties anyway.