You may not know but there have been three big "generations" of law systems. Many parliaments are starting to use fourth generation systems. Third and fourth generation systems look a lot like a complex git, but there are many things that should and do work differently.
When I started dealing with these things I thought that it was a solved problem, just use SVN (the cool kid at the time) and everything will be solved. Well, none of the existing versioning models work well with law documents, especially acts. The general ideas do apply, but many of the details do not. For example, just think of a merge conflict: who are you so solve a merge a conflict? What you have to do is to just record the conflict and create two parallel universes, one in which the conflict has been resolved using branch A and another one in which the conflict is resolved using branch B. You then keep these two universes alive and apply all the later changes twice. You have to do this until a judge or a legal body declares one of the "branches" the correct one; this may take years and the decision reverted (even partially) many times.
A few links to relevant standards and systems:
* Legal XML: http://www.legalxml.org/ An OASIS working group that is merging all the relevant national standards into a worldwide standard. * Akoma Ntoso: http://www.akomantoso.org/ A UN/DESA-sponsored format for legal documents. * CEN Metalex: http://www.leibnizcenter.org/ a meta-format that acts as an exchange format between legacy formats and new systems. * LexML: http://projeto.lexml.gov.br/documentacao/resumo-em-ingles A huge Akoma Ntoso-based repository of Brazilian laws. * ICA/SPP: http://www.ica.org/792/about-section-for-archives-of-parliam... The groups of archivists that deals with all the fine points you have to deal with when archiving laws and dealing with legal documents in general.
The main international conference on Law and IT is Jurix, it started in 1988. Check out their proceedings to see how things evolved over time.
If you are interested in hacking something related to laws or legal documents (judgements, parliamentary debate records, historical versions of laws) just get in contact with me.
Disclaimer: I work in this field and I am related to some of these systems.
In law systems derived from roman law (like in my country) law doesn't depend on judges decisions.
But IANAL.
You also need multiple contemporary universes whenever a law system has _favor rei_, i.e. the most favourable interpretation or version of the law is used while judging.