Once a BLM monument is set that is where the property corner is regardless if it matches a gps coordinate or not and everything in between two set monuments is prorated to the distance between said two monuments. So if there is two section corners and they should be 5280 feet apart but are either plus or minus lets say 10 feet then that section line that should have been 5280 is now either 5270 or 5290. Lets say that a monument is set that was set conventionally and was recovered using gps, it now has a gps coordinate. But a big earthquake happens and moves the monument 5 feet. Where that monument is, is still the property corner, it's just the distance and bearing to the next corner has now changed due to the earth shifting. The next surveyor will go and recovered the moved monument resulting in a different coordinate than past gps surveys.