[OakdaleMike]

I hate it when a thread like this doesn't conclude, so:

I followed dwanthny's advice above, and installed the Calibre binary for Linux on my Ubuntu office desktop. Unlike a couple of year's ago, when Kovid tried to help me and we both gave it up, it works without a hitch now. I set up this new version to Auto Add books from a separate Dropbox folder that I set up for the purpose.

I also followed his earlier suggestion and (on my laptop, not the webserving Calibre in my home office) temporarily changed the Calibre library to an empty folder set up for the purpose and added a couple of books, fixed up the metadata and converted them.

Then I copied the epub files to the Dropbox Auto Add folder. I noticed that a few moments later, the folder was indeed empty.

Pulled out my phone, opened Calibre Library, and found the new books!

Slick.

PS:

Well, if you follow my approach, please be careful. There are a number of warnings in this forum about using Dropbox and having multiple copies of Calibre open simultaneously. The way I'm operating, I violate this principle. I did, in fact, do some damage to my database -- all my epubs were still in my Dropbox folder, but Calibre didn't know about a few of the most recent. I repaired the situation by Auto Adding the missing books, one at a time.

I think it's OK to have two instances of Calibre running on two different computers only if you are very careful to be sure that Dropbox has completed syncing before you open the local copy (and to make sure sync has completed before you shut down that computer). My plan is to switch all but the webserving Calibre to a non-Dropbox local folder and avoid this issue. I'll still have local copies of all my books, thanks to the Dropbox sync feature and I can still use a local Calibre to add books using the above procedure.