Another update, a "good news - bad news" story.
Good news
I currently have a half dozen or so yellow squash developing (see comment below; all pots now dragged to a sunnier location, stems protected by aluminum foil). No squash vine borers (yet) on the yellow squash.
Bad news
One zucchini type surrendered to squash borers a couple days ago, stem rotted and collapsed overnight into disgusting orange mush.
On all of the other plants (in 10-gallon nursery pots), I moved them to a sunnier spot, and also tried another trick against vine borers, wrapping the stems in strips of aluminum foil (it is hard to do this completely with leaf stems and buds in the way).
I still had the last zucchini type get vine borers damage today. The plant had not collapsed, but the stem was open, so I fished around inside with tweezers and found the caterpillar, killed it (vine borers are moths). After, I covered the damaged stem with soil (part of recommended treatment if you do the "tweezer treatment").
We'll see how things progress from here. This is better than last year, but in the future, it is either don't grow summer squash at all, or grow tromboncinos (I have some tromboncinos already growing this year), or resort to more aggressive pest control.