Regarding 6.3.11, what vehicle is used to progress the undisputed value of Work in a Change Directive?
Although the CCDC 20 - 2008 A Guide to use of CCDC 2 - 2008 Stipulated Price Contract is now available at http://www.ccdc.org/downloads/index.html#guides, I have not yet got my copy.
However the CCDC 24 - 1996 A Guide to Model Forms and Support Documents also available at http://www.ccdc.org/downloads/index.html#guides, is still the current offering on the subject and is clear in the use a Change Directive.
I will post an article about this form next week, that I hope will answer your question.