Can you import a LR Classic CC catalog as a folder in a different LR catalog?

Hi all - Hoping someone can help me because I couldn't find the answer online or in the forum or tutorials.

Inexplicably 3 of my folder are missing from LR.  These folders contain folders and edits from the past 3 years (each year is it's own folder with subfolders).  There were extensive edits and flags throughout.  I have all the original files and I have a backup of the catalog that has these folders inside it, but it is from a month ago before I transferred all my files to a new hard drive.  I could reimport the images in the folders into my current LR catalog but I'd loose all the LR edits, etc...and it will take for bloody ever....

I see you can export a folder as a catalog so I though maybe I'd export it that way, but then I'd want to import that catalog folder into the a different/current LR catalog.  Is that possible, or is there another better way to get the catalog settings from those three missing folders into the proper LR?

I know I could just launch the backup catalog LR folder but then I'd loose all the imports and edits from the past month. 

Is there a way to combine an old catalog with a new one?

Suggestions?

And any ideas why these folders removed themselves?

Thanks!

Erin