Currently, when syncing book progress, an error is thrown if the book is not found in user books (i.e. user has not added the book into their "Want to Read" or "Reading" state:

13:50:04 INFO Processing target=hardcover book="The Count of Monte Cristo"
13:50:05 ERRO failed to update reading status target=hardcover book="The Count of Monte Cristo" error="Book not found in User Books - Skipping"

Requesting for a feature where the book is automatically set as reading if the book is not already in their tracked books.