Those are estimates, not measurements. The Earth is nowhere near uniform, so until someone tries a measurement you never know if the estimate's assumptions are right.

The effect is so tiny it is probably lost in the noise of other, larger, influences. The millisecond pulsar observers *might* but able to detect the change if they were running a serious of observations at the time.

In terms of preparedness and compass usage - an unrelated issue - the word is Slow. When a geologist says "a sudden pole reversal", "sudden" means thousands to millions of years.