AFAIK there are no 'Garageband CD's' included with the Logic Studio (Logic 9) upgrade or full version. Which discs do you mean?
If you mean the Apple Loops / Jam Packs discs then no these include ALL the Jam packs (including the Voices Jam Pack which is not included with Logic Pro 8).
Some of the audio content has changed, e.g. some warped settings for Space designer, etc. The majority of the content is the same though. So, if you perform an upgrade over a full Logic Pro 8 installation you will notice aprox. 2GB extra content & apps are installed on your system.
Hope that Helps,