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I think you're there. If you copied the ctb's into your current version's plot style folder, that's all you're supposed to have to do.
Maybe if you open the file in the new version's editor and do a Saveas. Does the Saved as file make your plots work correctly?
Agree with Tim, sounds like you did it all right.
We've been using the same CTB files since way before 2006, so there shouldn't be any versioning issues.
This Image may help.
And make sure the plot style table (see screen grab from post above, upper right corner points to the right CTB.