I suspect that (as tastes changed) the top was"flared" out and the base narrowed, changing the tiara from a more vertical circle (rather like a tube) to one which has a softer line outwards at the top. That would necessitate removing the solid and supporting lines at the top and would increase the distance between the elements enough that some additional stones and settings would be needed.
--Previous Message-- : : Kostenloses Bilderhosting : : In this comparison I highlighted some places : where diamonds have been added, so that the : diameter of the tiara would be increased at : the top. It must have been pretty : complicated to adapt the whole structure of : the tiara to a new shape. There must have : been at least the attention to wear it : again. : :