As the book uses the terms, they are not interchangeable. "Archive" refers to images which have been through ingestion and the Working pipeline and have been moved to their permanent home. After being put in the Archive, the files will not be physically moved again (until you upgrade storage.) It's not a backup. "Archive" is opposed to "Working" files, which are still moving through the Workflow pipeline (getting metadata and ratings added.) When an image has moved through all the steps of the Working pipeline, it moves into the next available bucket in the Archive and isn't in the Workflow pipeline anymore. Thanks to magic cataloging software, the metadata you added remains associated with it.
"Backup" is a duplication of your files so they can be recovered if lost or stolen. You want a Backup of Working files and also Archive files, since that represents your entire inventory of images.
I think the light bulb just came on. An archive is nothing more than an image in its permanent home. Therefore you only have two archives -- The RAW archives for non-destructively edited images, and the derivative archives for derivative images. in essence any image, original or derivative, appears in only one of three places -- working folder, RAW archive, or derivative archive.
The original camera raw file is backed up, but never archived.
Rereading the book with that in view is enlightening. It also makes thinking about the whole backup process much simpler.
The Virgin Download backup and/or pre-workflow backup is a separate issue. The ingestion moment is a vulnerable one, since the images aren't backed up anywhere yet and you are "touching" them when you do the transfer from the media card. If you want an extra layer of protection as you are downloading from the media card, you can have your ingestion tool do the download to two places -- into your Working folder to start the pipeline, and a Virgin Backup folder somewhere else, ideally on a separate drive in case something goes wrong with your computer holding the Working folder structure.
Thinking about this is much easier now, realizing this is a backup, not an archive.
Thanks for jumping in with just the clarification I needed!