This page contains links to various revisions of Intergroup Bylaws. The bylaws themselves prescribe that they be reviewed and possibly revised every three years. This has not always occurred on time. They were revised in 2012 (approved January 2013), apparently for the first time since 2004. They were revised again in 2015.
The bylaws specify that they be reviewed and possibly revised every three years. The next time that is to be done is 2018.