After years of collecting mainly Gottlieb and Williams machines I thought a perfect original glass was an extreme rarity. Then I picked up a Bow & Arrow with a near perfect glass. Thought I must have gotten lucky until I also got a Flip Flop, Hi-Deal and Night Rider with near perfect glass as well. Wow Bally figured something out during that era.
I thought someone stated at one time Bally used thicker glass. Theory was that it was less prone to expansion and contraction with temperature swings. Not sure if that is true?