Not the answer you require but I was operating the first dc10 flight across the North Pole; we were not allowed to to take the autopilot out of NAV but passing overhead the pole our NAV displays showed a 30 odd degree split - above 65? North each display was powered by a separate INS rather than the mean of the three.
Direct to on each side still left different tracks (next waypoint 326nm iirc).
We were planned Fairfax with enroute diversion to our destination ANC so we couldn’t afford mistakes as fuel was limited.
Fortunately we had a good moon so taking nav mode and watching the lat long readout we managed to intercept the correct longitude after 50 or 60 miles.
After a month or so the aircraft manufacturer came back that there was some sort of software issue which had now been rectified.
PS as you know all directions from the North Pole are south. Our Topo was courtesy of National geographic magazine circa 1985.
PPS I wasn’t quite old enough to have done a Nav course.