You'll need to open the backup catalogue. So be careful that when you open it, you don't overwrite your current catalogue.
In the backup catalogue, select the images and Ctrl S or Cmd S which saves your work back to the pictures. You can now remove the restored backup catalogue.
Back in the main catalogue, select the images and Metadata > read metadata from file.
PS I assume the 30 were removed by accident.
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).
Yes, it was an incorrect assumption and not really how Lightroom is designed. It can take many tens of thousands of images - just leave them in the catalogue.
File > Open Catalog will be fine in your circumstances. I was afraid you might do something else, but this menu command is safe enough.
Thanks for the advice and reassurance on the capacity of the Library. I'll try the suggested steps.
All worked well acc to your advice, for which my thanks. I will retain old files within Library.