OK, so you currently have X number of files on your exHD, some of which are being updated on your PC.
To ensure consistency, I would use your current backup app to restore the inactive projects to a folder called Inactive on your PC. This may sound a bit backwards, but I’d recommend doing this and then including both inactive and active projects from your PC in a single incremental backup job done by the one application, so all backup files are consistently readable.
Imagine, on your PC, you have your inactive project files in a folder called “Inactive” and your active projects in a folder called “Active”. Currently you have a backup of these these folders (Inactive and Active) on your exHD.
If it were me, I’d define an incremental backup job in CB that included the PC folders Active and Inactive, and schedule this job to be repeated at whatever interval I deemed necessary. The first time it runs, it would create folders on the exHD called Active and Inactive and perform a full backup of all the files in them on your PC.
You now have, on your exHD, two instances of all files in the PC folders Active and Inactive - one set previously created by your former backup app and one set newly created by CB.
As the files in the PC Inactive folder are not being updated, they will not be included in any subsequent incremental job. The only files that would be written to the exHD in a subsequent incremental backup job would be the files that had been updated in the PC Active folder.
At this point, the earlier instance of the exHD folders Active and Inactive are redundant, as the CB created exHD folders Active and Inactive contain ALL files.
I would not, however, delete the folders created by the older backup application just yet. I would make sure the CB scheduling works and works thoroughly. Once you are satisfied that CB is correctly performing incremental backups of changed files, the ORIGINAL exHD Active and Inactive folders can be archived to DVD and deleted from the exHD.
Hope this helps,