Thanks but it doesn't solve my issue - I would like to be able to see at a glance if I already have the book in some form, and if so what form - your suggestion simply produces lists which I could do in any number of ways. I would like to be able to look at an author and see 5 in hardcopy only, 3 others wanted, 15 ebooks etc. To give an example of a use for this, if I go to a secondhand bookshop (Barter Books here I come), I would like to be able to look at Calibre on my tablet and see if I already had a book, specifically wanted it, or didn't know it existed. With a substantial library in both paper and electrons, lists are simply unmanageable - I would need to convert the lists into books
(I feel a recursion coming on).
I also keep backups of my Calibre library and separate copies of all the originals (and backups of the discs they are on), it is just slightly irritating to have to use them, but more to the point, once I start to create empty entries, I can't distinguish between ones I have deliberately created and one that exist because I accidentally deleted the original format (I don't do it very often now, but even so Murphy's law being what it is, it will happen
On a separate note it seems strange to put feature requests in the bug section.