That doesn't appear to work. However what I did was remove the original copies from the working drive and synced the folder and subfolders, so hey showed as empty. Once they were removed from that drive and the catalog updated itself, the files showed up for syncing on the other archive drive and they would import and show up in the catalog for that drive. Something went wrong with the last update where the catalog which does not allow duplicate files to exist in one catalog.
Indeed, the option to import duplicate images has been removed from this version, which might be the reason for the issue that you are having here.
Hopefully they put it back in otherwise that means having a different
catalog for each drive which is a huge step backwards.