Thanks to E-junkieNinja for the offline suggestions today. I finally figured out why it wasn't working for me: The process described in the tutorial doesn't work for VARIATIONS, it only works for VARIANTS.
I just want to point out that this is an extremely confusing choice of terminology on E-junkie's part.
Also, while the tutorial content talks exclusively about VARIANTS, the title is misleadingly called, "How to convert Variants/Variations menus into a series of Add to Cart buttons". I don't see any content in it that shows it working with Variations, though, and my experience today is that it actually doesn't...
Anyhow, thanks again, everything is sorted.