Also confusing is that when I launch the latest version available to me, on launch Factorio has a popup which says I should select "experimental" beta in Factorio properties in Steam.
I believe you; I just feel like I'm getting mixed messages.

Ah. Thanks for that.

Might I then suggest updating the FAQ to remove the suggestion of getting the experimental beta? Here: viewtopic.php?f=49&t=4400

Cheers.

Hello;

Previously I was signed up for the latest experimental branch. I switched to 0.14.21, and can no longer switch back to experimental because the option is missing.
I rebooted my computer, logged into steam again, and it's still not working.
Factorio is not running, so that's not the problem ...