My bad! I was mixing up my books.
The Topaz book was a freebie (Lynn Austin, A Proper Pursuit) I had downloaded earlier, but for some reason its azw and mbp files got the same modified date/time as the Kelly.
The Topaz one *does* follow the no-size given rule:
Format: Kindle Edition
Print Length: 432 pages
Publisher: Bethany House (September 1, 2007)
Sold by: Amazon Digital Services
After posting here, I decided to experiment on the other item with today's date; that was really the Kelly, and I brought it into Calibre fine -- obviously with better info than the Austin, but I hadn't known what I should be looking for -- but then, on trying to convert, ran into the DRM issue.
I'll poke around for ways to break the DRM -- I'm aware it's possible, but for obvious reasons no one wants to point to the directions! And if it seems too complex for me, I'll be happy with the Kindle version.
Thanks for all the help!