I've installed Virutal Volumes View (VVV app) to catalog my 207 DVD and CD backups. (Well, actually, I've just cataloged about 75 so far). I like this solution for it's search and multi-platform capabilities.

This scenario involves a CentOS server with current working files, plus a separate "archive" drive, three laptops, and this collection of Optical Disks.

Typically, I backup projects as I complete them. However, now that I have this server, I've stored some archive files in this "archive" drive, and I've lost track of what is and what isn't backed up.

I'd like to find a way to use rsync plus VVV app to somehow script which files remain to be backed up. In fact, as I write this, I'm thinking I should convert this "archive" drive into "To Be Archived". I could do this with rsync, but I don't want to transfer files which have already been backed up.

How can I sort out what still needs to be backed up to DVD?

Not sure what you want to do - you're probably confused?

From what I've just read about VVV it just creates an online index of offline storage mediums.
You talk about using rsync and transferring files.