Thanks for your signature!
What a mess...
First find all files ending with the extension .lrcat . They are the catalogs.
By double clicking each one in turn, determine which catalog in your opinion is the most complete/up to date and take note of its name and where it is. I will call it The choosen Catalog below. Also try to notice if the missing images in each catalog are the same from catalog to catalog and in the Library module in the right pane expand Metadata and be sure to have the word All showing to the left of the word Metadata. Not far down under Metadata, you will see Metadata Date. This is the time of your last edit for the selected image and this can help you find in which catalog the information for missing images are the most up to date.
There are a couple routes we can take from this point. The easiest one is to fix missing images in the choosen catalog but there is no guarantee that their edits will be up to date. To do this, you can right click on the missing folders and choose to locate or click on the question mark of a missing image to locate. Images near those will be automatically fixed. The longest route is note the Metadata date for everything in each catalog and from the choosen catalog, import from catalog choosing only images with the most up to date information. Succes guaranteed but what a monks' work!
I would personnaly do this: Open the choosen catalog and go to the first missing folder or missing image and note the metadata date and close. By opening the other catalogs, see if they have more recent Metadata dates. If not, then just locate missing images and do the same for the next missing set. If you find more recent edits in another catalogue those images shall not be missing in that other catalog and if so locate them first, remember which catalog it is and close. Back to the choosen catalog, go to Menu-File-Import from Catalog... and navigate to that other catalog. Only choose the images with the more recent edits or their folder if all in this folder are similarly dated and import that. The information will be updated in your choosen catalog. Then, repeat the above steps as necessary.
You should now have your choosen catalog in proper order, anything missing and all up to date. Fine! Then close Lightroom and lets fix it as the catalog Lightroom will always open; Read all the following sentence before executing: Double-click the choosen catalog and immediately press the Cmd key. You should see a dialog box on which, if you look closely, there will be a check box in front of "Always use this Catalog". Check it. For sure if you double click another catalog in the future, that other catalog will open. But back clicking the Lightroom shortcut, it will open the one you choose.
Then, I suggest that you put aside all those .lrcat files keeping them somewhere just in case you missed something in the operation. Then, their corresponding Previews.lrdata can be trashed when you are definitely fixed.
Wish you courage and patience,
