A mess with my LR Catalogs and Keywords

[Heirloom Bob]

I was working on Lightroom Classic the other day and noticed two things,

My keyword tags were gone and I was NOT using the correct catalog version. I suspect this was all a result of moving photos to a different drive and various other tasks I messed up when I did those transfers.

So here is my dilemma. Is it possible merge all of my catalogs into a single new one if for no other reason than to get all photos into a single catalog going forward? Is that a reasonable strategy? I have a catalog Dec 2017 that contains 215,000 photos but they only go to 2016  with the last two years not showing. On the other hand, I have a catalog with another name but it contains 546,000 photos (which I don't think is accurate) It does have the missing 2017 and 2018 photos but they only amount to 35,000 shots thus my feeling the 546,000 is accurate.

I know that this mess is my on doing but now I am humbly looking for a possible solution to fix.

[JohanElzenga]

You can merge catalogs by selecting one as your main catalog and then use 'File - Import from Another Catalog' and select the other one. I can't comment on the number of photos.

[Heirloom Bob]

And when I merge, what happens with images that exist in both catalogs?

[SeanMcCormack]

Images remain where they currently are. The catalog you've selected as the main catalog will have references to all the photos from both. You may have to go tidy up after if you find you've duplicated photos but with one set missing.

[SeanMcCormack]

Also, if Lightroom detects that the files are the same files existing in both catalogs, it offers you an option to create virtual copies if the settings are different.

[JohanElzenga]

https://forums.adobe.com/people/Heirloom+Bob  wrote

And when I merge, what happens with images that exist in both catalogs?

You get some options for that. You can simply ignore this, copy the metadata and settings to the main catalog, or copy both those settings and the original file. If you choose to copy the metadata and settings, then you can check an option to preserve the existing ones in a virtual copy.