A single Lightroom catalog can support photos stored on multiple disks, even offline photos. If you want to move photos from one disk to another you can do the moves within Lightroom. If you choose to do the move in the OS then you can relink the photos. In short, it can all be done with a single catalog.
Now there are too many photos for a single disc, so I split them into two discs and created a new catalog to deal with the two different locations.
Let me also state that you don't want multiple catalogs in this case. This is a poor practice (even if you didn't have the problem you mentioned where your edits disappeared).
As Wolf said, move the desired photos in your operating system, then re-connect in Lightroom via that link.
Thank you Wolf and DJ. You both pointed me in the right direction, now all photos are in the catalog, edits included, and split between two discs. Much appreciated. --EdB