Quite likely Bret, the mileposts and engineers stations are two different things. At the start they were corresponding, but as time and the track progressed they drifted apart somewhat. In surveying it is not practical to start over if a mistake is found or the route is changed slightly, so an equation is put in showing the stationing up to that point and the revised stationing beyond it. Example: EQ. 243+76 bk. = 243+57 ahd., in this case showing an overlap of 19 feet. There could be a gap equation as well. Obviously, to do this with mileposts would be way too confusing. At any rate the mileposts are reference points and are not intended to a definitive distance. From an operating standpoint it would make sence to retain the same reference points, even if the distance is off.