Below is a limited timeline of resources that could be useful to researchers of the history of universal citation proposals, adoptions, and implementations.
The ABA Legal Technology Resource Center provided summaries of actions taken by courts on citation reform. This 2005 capture of the now-defunct website shows the following courts listed as having taken some official action, whether to allow or disallow some form of neutral citations: Arizona, Arkansas, Colorado, Louisiana, Maine, Mississippi, Montana, New Mexico, North Dakota, Oklahoma, South Dakota, Tennessee, Utah, Wisconsin, Wyoming, and the Sixth Circuit Court of Appeals.
This paper compares strengths and weaknesses of various states' implementations of universal citation recommendations as of 2006. Martin recommends these best practices that some states had already begun to apply:
In this 2010 blog post, Minick emphasizes the importance of a unique and permanent identifier for each court opinion, rather than a temporary slip opinion number, and highlights the approaches of North Dakota, Oklahoma, and New Mexico.