Long time coming but I did get back into my original file and test this…
Sure enough, simply toggling the lighting scenario on for my single persistent level caused the VLM to populate exactly as expected after a CPULM bake. I didn’t need to make a new, empty level and toggle on the scenario.
However, in the interim I did make a new, test file from a standard engine level template. I made a small room from engine content prefabs in the middle of the precanned landscape. Baking filled into VLM as expected on first try, no need to toggle on on create a lighting scenario level. So some files, my original included, will glitch and need LS turned on maybe? No idea what had been changed between the file being created and dressed before it came to me so I can’t really narrow it down more than that.
Also, baking in GPULM did populate the VLM as expected even without the scenario being turned on. Ultimately, I couldn’t use that method because it had a lot of leak and firefly issues of it’s own but for testing purposes it behaved as expected.
Thanks to all for input, especially you @am.glitch !