Being a longtime fan of Mary-Kate and Ashley Olsen means you probably know quite a bit about the child actors-turned- CFDA award winners . But even if you haven't subconsciously memorised every word of "You're Invited," never owned their Aquafresh toothpaste , and can't tell them apart — or, better still, know exactly how to (Ashley has a freckle on her upper lip ) — that doesn't mean you can't agree on one universally acknowledged truth about the twosome: They never change their style.