Hi Ian Hunter,
If you have just removed some files from Lightroom, you would be able to import them in Lightroom.
If you start working on one of your backup and then you will lose the edits you have done so far but that also can be recovered by merging the two catalogs together.
May I know what do you have to import when you go into the import window and select the folder from where you have removed some images?
I have 600 photos in this folder of which, approximately 200 are currently not visible in LR. I highlighted one photo to be removed but discovered that I had, in fact, highlighted two and I wanted to have one of them back. I can import straight from the current folder but, with 200 images removed images, it takes a little time to load all of them and then I have to pick the one I want. I have a folder into which I put the image I want to recover, then go to import images, navigate to the folder and select the image and re-import it into the original folder. It is such a long-winded way of recovering from a simple mistake that, I am certain, there is a quicker way of doing it.
No there is no other way to do that but if you have not made big changes to your catalog after your last backup apart from removing the folders then you can go back to the last back up you have created.
Thank you. Your help is appreciated and I will just have to be far more careful in future.
Regards and thank you again