Let me start by saying YMMV as to the success of MY method
Copy to Library is:
1) selective (per chosen books) vs by Library (Using the Export/Import tool)
2) It literally copies the Calibre DB ENTRY and Book, while Add has to read and Make a new entry
OK 2 computers. (remember my first statement above)
I violate the standard advice (for this task) on No Network shares
On the Old Computer Share the (path to) Library folder (if it is not already accessible from the new computer)
CALIBRE MUST NOT BE RUNNING ON OLD for the rest of the steps
On New:
Create/Switch: <path to Old Library over network>
Select books: Right click: Copy to Library <option>
DO NOT TRY AND MAKE ANY CHANGES TO THE REMOTE, that seems to be fragile. DO NOT TRY AND PUSH BOOKS FROM New to Remote .
OK
formats: false is how you find entries that have no books (AKA an empty book), these are also ones that you can not use ADD, since there is no book to read metadata from.
Unfortunately, I can't tell you how to find which books in the target (new) that are missing formats, while in the Old Library.
Create a CSV catalog from the results of Format: false (Catalog respects the view limits)