I don't know a lot on the topic but the position of the magnetic pole have always been roughly located in the same region for the last couple centuries. Moving slowly so that people could not notice the changes until recently due to some technology, I presume.

A polar inversion is possible, where the north and south switches position over a certain period of time. If that happens, the compass will point to the south pole.
A weakening of the magnetic field is also possible. In that case, several pairs of poles could form. The compass will indicate the closest ''north'' poles, and it can be located anywhere on the planet.

I don't know how fast the changes can occur and nobody would try to create a navigation system on something that random and slow.

Sailors can also relies on the position of the stars o indicate their position using a sextant for example.