The tricky part is establishing a 1st point that is unchangeable

100% right, Flatlander.

Over 25 years ago a client was financing property on Long Island whose legal description began "at the northeast corner of the intersection of Plum and Main Streets". My conversation with the title insurer went along these lines:
me: Please specify the location of these streets by referencing the original recorded plats dedicating them.
them: There's no such document of record; these streets date back to colonial times.
me: Then how can one know where that intersection-point is?
them: By going out to the street-corner and looking, of course, silly!
me: But if the streets are widened in the future, how will we then know what point was intended?
them: If that happens, so what? We are insuring that the mortgage you have is a valid lien on the land.
me: Yes, but over *what* land? How will we know what land is subject to the insurance?

Eventually they had to specify the point by reference to the rudimentary set of "cadastral" points they had available -- complicated by the fact that their cadastral measurements were based on magnetic north, while their other measurements were based on true north.