Originally Posted by user_none
I'm not asking to be snarky but does the book entry contain formats other than MOBI?
Yes. I always ensure that each of my ebooks have more formats than MOBI, since converting a file to overwrite itself with no other available formats makes the changes permanent.
...Which is to say that when I put books from Amazon on Calibre, I add them as AZW. When I download books from fanfiction.net (using FLAG webservice) and add them to Calibre, I do so as EPUB.
So then all of my ebooks have either EPUB, AZW or some other format as well as all having MOBI (which is what I upload to my Kindle.) In this way, I always have the original
version of the ebook from which to use in converting to the format I put on my Kindle.