Guys - providing you are prepared to accept that a modern inertial platform has VERY FEW errors, please accept that True North is NOT 'updated' at any time (without an alignment) but merely 'maintained. If you ran a platform for several days without an alignment then the errors would obviously would accumulate. We have moved on from gyros spun up with string sitting on top of a miniature Eiffel Tower
Also bear in mind that a difference of 0.1 degrees would not have any noticeable effect on your displayed heading, attitude, nor on navigation, especially since
position is constantly updated whenever in range of the required signals. You just would not notice 0.1 degrees UNLESS you look at the displayed heading data.
NB Vastly simplified for simplicity!!
The effect of a 0.1 degree error in true north would simply mean that all the electronic 'fudges' applied to the platform 'attitude' to compensate for earth rotation would be in error by 0.1 degrees - not a lot! Looking at a platform at the equator with the platform 'pointing' north, the electronically 'applied' platform roll rate, for example, instead of 15 degrees/hour would be in error by 15*sine 0.1degrees. Not a lot! I make that 0.02618 degrees per hour. Thus in simple terms, after 10 hours, the indicated bank angle would be out by 0.2618 degrees. Even I cannot fly to that accuracy. I don't think you would fail your IR renewal on that.