I knew posting a "hesitant success story" was bad luck!
After inspecting my daughters' bunk beds this morning, I found a black dot on one bed slat. It's a perfect circle, flat, and when I wiped it with a wet cloth, it did not smear. The bed is currently painted with Kilz. Would fecal matter still smear on that kind of paint? All spots we had found in the past were raised slightly and would smear when wiped.