Restoring old catalogs, combining with catalogs?

[hyycc]

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?

[ManiacJoe]

You have the right idea.

Find an old catalog that contains the old photos you want.

Open the old catalog using the new LrC to upgrade the catalog.

Verify that this upgraded catalog has the photos you want and properly locates the images.

Open your current master catalog, make a backup just in case.

"Import" the upgraded catalog into the current master catalog.

There may be some details you might have questions about. Feel free to ask.

The backup of your master catalog is important in case something goes wrong.

Which version of the Mac OS?

[hyycc]

iMac is Big Sur, 11.7.6.

MacBook Pro is Monterey, 12.6.5.

The other wrinkle is to get a RAID and host the libraries there, so I'd have to change all the paths.

[hyycc]

Some subset of my RAW files have matching .xmp files.

These should have all the edits.  So instead of trying to restore and combine old catalogs, for these I should just be able to reimport and it will have edits, keywords, ratings?

In which case it's only the NEF files which don't have matching xmp files for which I'd have to find the catalog?