I am a civil engineer with limited site survey experience. I have been reviewing the various NAD adjustments such as NAD83(2011), NAD83(HARN), etc. and have a question. I understand the differences between these adjustments does not constitute a change in the ellipsoid. It sounds like the adjustments are more about the method data is collected, not about the ellipsoid. The adjustments appear to involve more accuracy reference networks, additional base stations and networks added, not so much of changes to the ellipsoid. If my understanding is correct, how do the adjustments impact the ellipsoid, if the ellipsoid does not actually change ?