Restoring old catalogs, combining with catalogs?

I have two separate directories, actually two different drives where I've stored LR libraries.

Over the years, with various upgrades of LRC, I've had to rebuild catalogs, including at least one time being guided to rebuild them because a newer version would not launch.

As a result, the more recent directory is tied to the current catalog I'm using but my older directory, with about 3 TB of RAW files, isn't known by LRC at all.

In fact I think originally I had that older directory on another volume and the ones I have now (on two separate drives) represent copies from the original because when I open LRC, it references old volumes that I no longer have -- changed the names.

If I tried to reimport the old directory, I wouldn't get any of the edits or metadata, all the hundreds of hours of work I put in.

So I'm assuming I would have to restore an older catalog file from one of the many LRC backup directories that I still have.  I may also have Time Machine backups which go back 5 years or so.

Then load one of these old catalog files, probably let the current version of LRC update the catalog file, and hope that it recognizes all the RAWs in the old directory?

Then once I'm satisfied that I got all the metadata and edits of the old directory library, I would look to merge it somehow with the catalog of the newer library directory?