Thanks. Seems I was being too anal (that has never happened before

Luckily, most of the originals were pdfs, only a handful of epub, and I used Mobipocket Creator to convert to mobi. I see it makes a file in My Publications, and the original format is right there! I back up Calibre 3 ways now, including dropbox, and will make sure to keep the pdf in the folder that gets backed up.
As always, thanks MobileRead!