looks like post build date sep 2008 was the first offering. Makes since since Mike Miller and others in the CCA state that september is the time when the lines get reset or retooled for changes. Production runs vary based on model & birth place (munich, Regensburg, ect ect ect).
oddly wikipedia has a good write up.
http://en.wikipedia.org/wiki/IDrive#...tion_.28CIC.29