Hallelujah !
Thanks to BetterRed and DaltonST I think I am now out of the woods. A very real "Thank you" to all of you.
In the process I was taught quite a bit about the capabilities of Calibre, although I have no doubt that there is one heck of a lot that I am still totally ignorant about.
So in a few days I've gone from four unequal Calibre libraries ranging from a Largest of 11,294 books down to Smallest of 10,157 books to four pretty equal libraries of 12,686 books each.
As I said, "Thank you" to everyone,
Cheers,
Brainless, but beaming, Basil