So I went back and reread all the instructions in all the books, and pondered all of the suggestions and methods in the past thread (which I can't get to at the moment. When I go back, I get a 404 error.)
Instructions say to pack firmly, but not to tightly...and one person said they poke their cabbage daily with a skewer. So I'm thinking maybe it's packed to tightly, and maybe I've got more weight than I need on top of the cabbage.
So I checked that out, and when I poked into the cabbage, great bubbles of cabbage belches arose. So, hmmm....there's bubbles happening, but they aren't rising to the top like I expect. So I put a plate back on top, make sure the liquid level is good, and put one jar on top to the hold the plate down. I figured that I'd check again in a day and see if more bubbles had formed, or if the bubbles I just released had been trapped a long time.
So again today I poked and prodded, and again I got a lot of bubbles.
So my new hypothesis is that this must be yet another quirk of living at high altitude. For whatever reason, the bubbles aren't finding their way to the surface the way I expected them to, but they are forming down below. After this last poking, the looser cabbage was a little higher in the containter, so I added more salt water per the Ball book's instructions. I'll poke it again daily, of that's what I have to do, but at least now I know that something's going on down there.