Since your menu for "open recent" has multiple catalogs listed in it, you should open each one and verify that you are not just looking at the wrong catalog.
The files with the LrCat extensions are your Lightroom catalogs.
When you did the export, did you choose "export" meaning to let your edits be seen outside of Lighroom by creating new JPG files to contain your edits?
Or did you choose "export as catalog"?
Your back up of the original files will never be referenced by Lightroom because they are the emergency backup and should only be restored from in an emergency.
I thank you, desperately, for your reply, ManiacJoe. I'm still very confused. My main concern is why all of a sudden three folders, imported on various days in 2017, are no longer listed under all my listings of 2016 in the left side of the screen under my external drive's listing.And there's no listing of the collections.
Of the "open recent" menu listings, the two collections I made are listed as Nameoffolder ircat. The rest of my recent catalog listings, none of them from 2017 and none of them collections,, list as "nameofffolder lightroom5ircat". When I click on collections listing, they say to relaunch using the thumb drive I exported them to. When I click the others, they also say I should relaunch (thought not to the thumb drive). Is it safe to relaunch (I can't find the word in my instruction books) and is it safe to relaunch from a thumb drive? And what will opening these files accomplish?
As for exporting the collections, I think I used export as catalog.
Part of the problem seems to be that you have way too many catalogs. Most of these problems disappear if you have a single catalog.
I agree with ManiacJoe, you most likely have opened the wrong catalog. If File->Open Recent doesn't find the right catalog, then you need to use your operating system's search feature to search ALL of your hard disks for files whose name ends with .LRCAT (not .ircat) and double-click on each one found until you find the one that has the photos/collections of interest.
Thanks for your help, Mr or ms Paige. I relaunched all my catalog listings and found all the files I wanted but one.I was unaware that I was creating more than one catalog. I thought that when you imported pictures into your external drive and you sent them to one folder, you were not creating a new catalog. Do you have by chance a sentence or two on commons mistakes regarding importing and creating unnecessary catalogs? Or is it something that is explained obviously and clearly in instruction books?
The only thing I can tell you is that sometimes people create new catalogs by accident. This would not happen in the Import step, but rather when you launched Lightroom you got the wrong catalog or a new catalog, or perhaps you accidentally selected the menu command File->New Catalog. Beyond that, I don't really know how people accidentally create new catalogs.