From the wonderful book Vintage Fashion I've learned a lot of things: one is that not all vintage sequins are created equal. The first version of these light-catching baubles were made of gelatin.
Gelatin sequins were subject to damage readily than their modern plastic counterparts. According to the book, it's possible to find vintage frocks with ghostly handprints where the sequins had been--they had simply melted away under the warmth of the hands of a dance partner.
I can't think of a more romantic way to ruin a dress . . .