Thank you both for replying to my thread.
The best and easiest way to archive parts of a calibre library is to emulate how the books are stored in the calibre library. One folder per author and in those one folder per title. And cover and OPF-files saved along with the different formats. Then it should be easy to restore all the books and most metadata if you have to add the books back to calibre.
I saved the data using Calibre and my list of books has all the books under the author's name.
There are about 100 authors. I have tried all the selections on the top right and the best I can do is one author (and all the contents of the file) at a time.
I was hoping I could move bulk authors back into a library rather than going through each author.