I think you are right. Perhaps there were a form/letter together with the CDs, and sending the form to Garmin they will send you back the new CDs?
When I bought my CS, the packet included the v7 CDs. I remember that - at least during the last spring - there were a form awailable on the Garmin site, by which you could order the update.
I would simply send a message to Garmin (there shoudl be contact details and -forms available on their site).
You may also try this newsgroup: sci.geo.satellite-nav
For me the version 7 was a must, as it is the first one covering the whole Finland (from where I am) and Norway (which has really nice mountain roads). I hope the next version will soon cover easter European countries, too. Poland and Czech there will be, but Baltic countries are also on my wishing list.