[JoeC]

James - There is no XX on the sheets. I did not mean that the "XX" is on the build sheet. I just put the XX in my post to show that there should be two letters there. From what I read the two letters were ECL codes (Exception Control Letter). GM used the letter change to show a variation or update was made to an option number. Instead of changing the numbers to show a change they would start out with an "AA" and bump up the letters for each change even if it was just a price increase. The letters probably have additional meanings. We use a three letter system where I work to show engineering changes or software changes. In our system one of the three letters is bumped up according to the type of change that was made. This is why the ECLs would jump from AA-BA then CD-CE. The ECLs are also used on RPOs. They are on many GM documents such as window stickers ,shipping documents, broadcast sheets, etc. Engineering needs to document any changes to aid product assembly and field service.