Data Hoarder

I truly understood the 3-2-1 backup rule and I'm trying to stick with it. The thing bothers me is that, those drives are all cold storage drives and I only connect those when I have new stuff to backup.

Now I have different sets of data with different levels of backup safety, and it's really hard to manage. I use SyncBackPro to do direct sync of the same copy (In different drives) to keep the data in sync. Since Raid is not a backup, I'd not choose the Raid1 mirroring solution. My drives have historically reasons to be in different sizes... (sigh)

Now the cold storage disks are laying around waiting for me to manually sync data sets one by one, and I already have a hard time keeping track which sets of copy is already on which disk. (I can only connect 2 drives at the same time, maybe NAS could help?)

How can I easily manage the backup synchronization and if not, at least having a better way to mark down which set is already on drive A, B, C at the same time? I hate updating data and synced between drive A and B, then mark it on the folder to remind myself to sync to drive C when I connect drive C in the future? Also hate manual data tracking with excel...e.g

In drive A (folder names I'm using):
Data 001 - [A, B] -> The data set exist in drive A and drive B
Data 002 - [A, B, C]
Data 003 - [A, B, D]
Data 004 - [A, C, D]

In drive B
Data 001 - [A, B]
Data 005 - [B, C, D]