PSE 14

I can't ignore your initial post because it may provide a solution to the problem of finding the missing photos of your niece. 

So, as I understand it, you have some photos of your niece that were in your catalog, but are now missing.  Those photos are dated 5/30/84.  I also assume that you have several backups of your catalog that have been created.  If my understanding is correct try the following to find the missing photos:

• Open one of the backup folders that should have your missing photos in Windows File Explorer (or the Mac equivalent if you are on a Mac)
• Click on the Date Modified column to place the files in date order
• Scroll through the date column until you get to 5/30/84 and click on the photo files with that date.

Are your niece's photos there?  If so, copy them to the folder where they should be.  In fact, if you know the folder where the files should be, that is where you should start looking for them.

I'm not stumped yet, but you really aren't giving us enough information.  Your initial question was:

Is it a bad idea to combine ALL of my last 5 back up files into one HUGE file?

I don't know what this question means.   I also don't know whether you are asking about something you have already done which may have contributed to your second issue which is what happened to the files of your niece.  Or whether you have some other plan (which on the face of it doesn't sound like a good idea at all).

You also ask Could this prevent the "searching for file" pop up?  This suggested to me that you have already been having searching for file pop ups.  But, again, you haven't given us any details.

So what exactly are the questions you are posing?

I have no idea what you are proposing to do.  Clearly you have some problems that need to be fixed before you do anything else.

The searching for file message is popping up because you have missing files in the catalog.  A file will become missing if you have undertaken some file management (delete, move or rename) outside of the Organizer.  All file management must be undertaken within the catalog or you will run into problems like this. 

I highly recommend that you reconnect all missing files before performing any backup action.  If you don't, the backup is likely to fail.  Even if the backup completes, it may fail if you try to restore it. 

I suggest that you go to the Find menu and click on All Missing Files.  This will search for all missing files in your catalog and will present them in the grid.  The number of missing files will also be shown in the lower left status bar.  Hopefully, this will provide you with some clue as to why the files are missing.

Please explain further what your main question is and why you want to do whatever it is you want to do.

@Bulza 

I have moved your post from Photoshop to the Photoshop Elements forum where you are more likely to get assistance.

Jane