It was decided long ago that GPS coordinates cannot be the only definition of the location of the start, finish, or turn-around on a certification map. It was clarified at an annual meeting a few years ago that this also includes ANY point that defines the length of the course, such as the location of a turn point.
The fact that you can set up a large number of flags to define your route, and then use those to ride the course two times and get less than 0.08% difference is only one small part of repeatability. The real test is for another measurer to set up the course 3 months later based on your description, and then ride it and get with 0.08% of your measurement.