The current edition is from 2008, and revisions to the guide come about in one of two ways. Either the Prime Minister asks us to sit down and revisit it, or we suggest to the Prime Minister that it may be time to revisit it because certain things have changed. Normally when there is a change in Prime Minister, they want to take an examination of the guide, as it is their statement to their ministry of their expectations. Those are typically the triggering events for when changes can occur to the guide.
On November 17th, 2009. See this statement in context.