Tolerances of a couple milimeters? Ha. I hold .005" on bent sheetmetal parts WITHOUT coining it. I can hold .001 if I coin it. Machined/milled tolerances can be held out to six places without much effort and that's using an old 1943 vintage lathe.
Even shipbuilding scale work has tolerances closer than "a couple of millimeters."
I suspect we're looking at tolerances of over a hundred decimal places or more by the time the Galaxy Classes are built.