Here's a weird idea- When real fashion from a specific time period becomes "a costume" when it's used in a performance?

Then a designer decides 

to use a sleeve or a silhouette for part of their collection and suddenly its fashion all over again. 

.

Pippa has much more in store for you so please check back. 
Look at silhouette (shape) of  each dress.
Can you describe the 
fabric?  (heavy, light, decorated, plain, expensive,
everyday, )
do you see any similarities?