Actually the the monument is exactly where it is supposed to be and at the true corner of the 4 states. It is right over the sandstone shaft marker placed by the original surveyor commissioned by the federal government in the 1860's. Although due to the accuracy of surveying equipment available at that time, the use of previously established surveying data & markers, the difficulties involved due to conditions and terrain there is only an error of 1800 feet of where it "should be" not 2.5 miles. It could be even be considerably less that 1800 ft.
Although there may be errors in the govt surveys, once the survey and marker are established and all parties accept them they are official. So when standing on the marker you are in fact in all 4 states at the same time. No one is being ripped off by the monument being in a false location. Where it should have been has no bearing on what has been established and recognized by law.
https://www.ngs.noaa.gov/INFO/fourcorners.shtml
