This occurred because at some stage the plunger was changed. I do have examples of both stems, but not of the 18-seg inner, so that's another interesting development. The outer mould must also have been changed at some stage, so probably Chance was just tweaking the design as it went along (moulds, even cast-iron ones, did not last for ever). The other point is that the sundae glass is not one of the commoner shapes so there are not many examples to compare - I have green-, blue-banded and clear examples.