When/how to backup metadata changes

I'll re-read the relevant sections in the book tonight, but today I was diagramming out the flow of files from camera ingestion to final product, and I got a bit confused as to how to handle some of the offline media backups.

At this point I don't shoot raw (not a well supported format for my camera), so the workflow has been simplified for JPG-only. However, I expect the same issue would apply to the workflow Peter lays out once you've got your DNGs into the catalog app.

1. Import from camera to disk, rename (on-the--fly or separate step, doesn't matter), put into bucket RAW_0001
2. Make backup of bucket to external drive
3. Import into iView, do some keywording and create virtual sets
4. Repeat until bucket is full
... (time passes)
5. Burn bucket to CD/DVD

Ok, so far so good. But now what do I do if I add more keywords to photos that are in buckets that have been burned to offline media? Do I re-burn an entire bucket, even if only some of the files within it have had keywords added? Is there some threshold?

Or do I rely on mirror backups of the mainline buckets to keep my metadata safe? Then it seems there's a gap between the online backup and the offline backup - if both should fail catestrophically and I only have the offline backup, I've lost any metadata added since the bucket was burned (which is controlled by shooting volume).

A parallel question for the master/derivatives "branch" of buckets. You'll burn those off to CD/DVD once you've got enough in the bucket, but if you revisit and edit files that are in buckets that have been burned do you re-burn the bucket? Do you duplicate the file into the current bucket and only work on that one going forward?

--Jason