If I may be so bold - what Dodge Man is saying is that a survey is a rendered opinion. This is true, both literally, and in any court of law. We like to think that because GPS and other gear can provide pinpoint accuracy, which it can, that surveys are super accurate and there should be no issue.
The equipment, provided the surveyor chooses the better stuff and takes the time (this equates to a more expensive survey) can measure a point as tiny as a gnats butt, to a repeatable accuracy within an area the size of a beer can. But that doesn't necessarily equate to an accurate survey. Why not?
The answer lies in history - there is no virgin land. By that I mean that a surveyor is working from historical documents, as did every surveyor before him, except for the schlub who shot the first traverse in that area. And that was likely several hundred years ago. Those documents, especially the earlier ones, are the product of both lesser equipment, local politics, and the abilities of the surveyor doing the work.
A professional survey is rendered opinon that is the result of following established rigorous practice and method, and should always be understood as being a 'best fit'.
You don't really think that jet airplane you are flying in REALLY knows EXACTLY where he is all of the time?

If he uses only GPS, he doesn't.
Big Al