Transfer options: Copy Snapshots, Media Verification, Match source Catalog File to destination Catalog File, Don't add duplicates to Backup Set.
My transfer scripts are Recycle transfers, and the backups on the source set were created with "Don't add duplicates to Backup Set" turned on. The only difference between the original backup settings and the transfer settings is that the original backup has "Match only files in same location" turned on, while this option is off in the transfer. I guess this *should* result in less data being transferred than was originally backed up, because of the scenario you outlined, where OS files on different systems would not be copied multiple times, but what I still don't understand is why a transfer of a 3-tape set always requires 3 tapes in the destination set, even when the amount of data reported verified in the log should easily have fit on 2 tapes...
Operations log example: Under Transferring, it says "Completed: 3303458 files, 2,124.3 GB." Then under Verifying, it says "Completed: 2679494 files, 1,567.8 GB." The Verifying section has "Execution completed successfully," which is nice to see, but the very next line is "Remaining: 1 files, 281.8 MB," which doesn't exactly inspire confidence...it verifies all but the last file? Or all but the last 600,000+ files??