(friggin' closet Jerbiton.
[shakes fist at heavens]
There will be NO COMPROMISE!)
(Ok, thought about it. Here we go...)
[color=darkred](Note - The Rules stem from the Laws, but reinterpret them to fit the Game, re balance etc. Readers should keep this always in mind, that there is a distinction between the Laws, and the Rules that spring from them. If there is a contradiction, StoryGuides should use their common sense, or just follow the Rules, depending on your own essential nature.)
The Law of Sympathy is mainly one of symbolism. A feather can represent a bird (any bird), and a stone can represent a castle (if poorly.) Voodoo dolls and such are another classic example. When actually made from an object that came from the thing they represent, the Law of Contagion adds strength to that representation.
The Law of Contagion is, indeed, what we are mainly addressing here. These Laws are not included in the Rules, and so it seems the original wording of the law has become generalized.
Not quite. You're using the wording of the rules to rephrase the Law, which then changes the reading of the rules.
At its simplest, the Law of Contagion is: "Once together, always together." At length, it can be expanded to imply that when two things are in contact, there exists an astral bond between them that is not lost when they are separated, such that actions taken on one can effect the other.
It has nothing to do with Parts subservient to Wholes, nor Platonic Philosophy, unless that is an Ars re-interpretation (which may be a valid and necessary evil. If that's so, then never mind.)
The Law of Contagion says that if the two halves of the rock were touching, especially if they were connected, and (what's stronger than "especially"? ) extra-double-especially if they were one, then when split in half, they are still connected to each other.
Now, as written, the Rules do not emphasize "contact" or touching, but "an association", which is a partial extension of "Once together, always together."* The two halves of the rock are, and always will be, directly associated with each other, and so are now AC's to each other, despite the original "whole rock" not existing in the philophical sense.
(* So, a favorite toy is an AC to a child, even tho' they were never part of a single discrete, permanently connected thing.)
(Now, I found an interesting quibble, that says that if hair is cut from a person, and then that person cuts their hair again, that first part loses it's connection to the person, because it was only "together" with the now-missing intermediary piece. By this interpretation, one would simply have to polish the broken surface of one half of the stone to break the connection. But I'd submit that the association still exists, despite the technicality, from the Law of Sympathy, if not narrowly defined Contagion.)
So, we look at the simplest wording of the Law of Contagion, "Once together, always together", and ask ourselves: Was the magi ever "together" with their hair? Simplest answer: Yes.
Once together, always together. (Rules about degrading over time notwithstanding.)
(Getting back to the original question, were the original individual pawns of vis ever "together" with each other? Tougher question, especially with an eye to the "association" issue of the rules. I'd say "no", no more than any two neighbors are "together", in this sense.)
Now, the Rules, for game balance, often do reinterpret or modify such absolute laws, and for various good reasons. And SG's should always do the same, with a mind to their own sagas and ongoing stories, short and long-term. But, in the absence of such canon or individual interpretation, and keeping in mind the Rules vs. the Law, I'd say it looks like a two way street.