Understand on the confusion.
For us it's a little different because we publish to codeplex and then to MSDN and print.
So for us it's been
BETA1 ->BETA2 ->RC->CTP (All done on Codeplex) -->MSDN and print
So you can consider that the content is stable in the CTP, but that it's not "official" until it appears on MSDN and in Print.
The Summer 2009 is due to the time it takes to prepare the content for print form.
If any changes come, it would be to make the content more suitable for print form. To my knowledge as one of the authors, there are no technical changes that are slated to occur.