It was just another of the many strange and mysterious things done by lantern manufacturers. The pivot in the bail was not a new idea; it came and went with several companies. You can find pivoted bails as far back as the 1887 Ham #00 which gave up the pivot when it became the Gem. Before their lanterns had production dates, Dietz made small detail changes just to mark their production runs. But it's lucky for us that they did that because it gives us a visual way to date the lanterns. BB