Previously importCatalog and finder folder lists don’t match and many are not there-but not missing

I have folders by year which show in LRC catalog but are empty, not missing (no question mark) but which contain a full listing of files in my photo storage on an external hdd and are actual photos files. How can I get these folders to show the individual files in Lightroom again. Is this an opportunity to use the dreaded synch folders?

In addition to 6 years that aren't there, I have 12 or so that seem to be normal and contain all of their files. Does this make any sense?

Back story: I created a temp catalog for a long vacation so that I wouldn't have to back-up my quite large catalog, with the idea that I would merge the 2 when I return. Somehow I ended up with 2 master catalogs and 2 temp travel ones. Ihaven"t had any luck locating the lost folder contents but think that may be where they are. How can I locate them?

Any help would be very much appreciated. I will respond as quickly as my sporatic internet in centrat Canada will allow!