"The plants look good otherwise. They've climbed vigorously and have lots of blossoms. "

To me this is the key. The few yellow leaves are not affecting the crop so, personally, I would not worry. The bottom leaves of my climbing beans always get eaten by snails and slugs but as long as there are plenty of beans it doesn't bother me.

That's reassuring--thanks! Now they have lots of beans, Lots of Japanese beetles too, but their bean production doesn't seem to be affected, at least at this point.

Not sure how worried you need to be about Japanese beetles. We don't get them here. I was only referring to the yellowing lower leaves.