I was curious about the origin. You wrote "Elio Fiorucci invented the modern skinny jean in the 1970s".
What makes something a "modern skinny jean"?
That is, I did a quick (and non-exhaustive) search of archive.org and found an advertisement in the UCLA Daily Bruin from January 15, 1971, on the bottom left corner of page 16, at https://archive.org/details/ucladailybruin55losa/page/n89/mo... .
"""Newest body decorations. Skinny jeans with just the right flare. Low-rise. Scoop-front pockets. Sharp, multi-color stripes in a bunch of different widths for whatever is in your head. Permanent press Fortrel® polyester and cotton. $9"""
These are not made of elastane.
OTOH, https://en.wikipedia.org/wiki/Slim-fit_pants#The_1960s says that in the 1960s, "By 1962, Sears were selling tight jeans made from "stretch" denim that incorporated elastane."
So, what defines the modern skinny jean different from pre-Fiorucci skinny jeans?