DJ Flyboy Don’t confuse the two limitations.
1. Alignment. Most IRSs can’t align above the low 80s N/S as there is not enough change in velocity to align the gyro. Think a gyro at the pole is just rotating like a record player. These limitations are invariant of hemisphere.
2. Operational areas that give accurate mag track for the ADIRUs. This is dependant on the magnetic variation tables which are no symmetrical in each hemisphere.