Thanks for that advice. My 'backup' LRCAT is on a remote drive (accessible from my desktop). Can you give a little guidance on how to 'open' that backup catalogue, please so I do not upset anything else.
The 30 photos were 'Removed' intentionally by me to 'clear' the unused images cluttering up my Library. I thought it would be easy just to call them up again (after being Removed), but it seems that was a incorrect assumption. I do have ability to re-iport the RAW images into the folder in my Library (without any further processing during the Import).