Interesting problem. Several things come to mind:
1) The Pragmatic tip "Keep knowledge in Plain Text" (fro the Pragmatic Programmer book, that also brought us DRY). You can argue whether XML, JSON, etc are considered 'plain text', but the spirit is simple - data is open when it is usable.
2) tools like diff and patch. If you make a change, you need to be able to extract that change from the whole and give it to other people.
3) Version control tools to manage the complexity of forking, branching, merging, and otherwise dealing with all the many little 'diffs' people will create. Git is an awesoe decentralized tool for this.
4) Open databases. Not just SQL databases like Postgres and MySQL, but other database types for other data structures like CouchDB, Mulgara, etc.
All of these things come with the poer to help address this problem, but come with a barrier to entry in that their use requires skill not just in the tool, but in the problem space of 'data management'.
The problem of data management, as well as the job to point to one set as 'canonical' should be in the hands of someone capable of doing the work. PErhaps there is a skillset worth defining here - some offshoot of library sciences?