A few books on Kindle not showing up in Calibre
 

I have the K3 Keyboard. I have transferred books a couple dozen times over the past year without issues. I have a new problem recently.

Two books are on the main page of my Kindle and I can read them, but when I plug in via USB, they aren't in the list under Device. All of the other books are there, but not these two. I searched and searched.

Can I copy them another way and manually add them to Calibre? I don't really need a backup of these two but I am curious in case it happens with a book I want to backup.

Download them from the "Manage my Kindle" page on amazon.com