You didn't overwrite any defaults. The "defaults" are just that - default values for new Projects you created. They have nothing to do with existing Projects.
When you move an existing Project to a new version of TMG the paths set in it are left intact. That's the whole reason for having paths in the project, so each project can have it's own paths and you can keep everything separate for different Projects if you want.
Your Project now in TMG 9 is using the old exhibit paths because of one or more of the following:
- You never moved the exhibit files to a new location.
- You never told TMG to find the existing files in their new location.
- You never told TMG to put new exhibits in the new location.
Only this last is accomplished by changing the path in Preferences > Current Project Options > Advanced.
See may article on Moving Data to New Computer or Version for details on how to do all three.
In my opinion putting exhibit files in the default location, under a version-specific folder, is a poor choice. If they had been placed in a "version-neutral" location you wouldn't need to deal with this in the course of an upgrade.
BTW, you should check the other paths, not just the one for exhibits, because they too will remain as before, which may not be what you want if you have used the default locations for them.