I would find a backup of the primary catalog that contains the missing folders. Then transfer those from the backup to the merged catalog.
Thanks for the reply dj.
I do have a backup that includes the missing folders containing edited images but I don't know what you mean by transfer. I know that I can import the images but I am sure that will require reediting the images. I have looked at adding a folder from the folder panel of the Library module but that does not seem like a solution. Could you be more specific?
Actually, it's the same thing you did before to merge two catalogs.
You select the 8 missing folders, right-click and select Export This Folder as Catalog, then in the other catalog, use File->Import from Another Catalog
Thank you again, dj,
Since I don't understand how this problem developed, I am a little reluctant to merge a second time. Additionally, it will be only slightly more time consuming to import the images again. I do appreciate your help.
The time that it takes to import is not the issue. The issue is that when you import, you lose some or all of your metadata and edits.