I believe that facial expressions and body language are slightly changing from decade to decade, same as fashion, trends, slang etc Example: watch a comedy from the 50's and then a comedy from 2012, and you will notice that expressions have changed.
Do you agree with me? Do you see a difference?
I thought of this as I was taking the Baron-Cohen eye test. The pics are from the 50's mostly I think and 60's, I was not born then, and that's maybe why the expressions were so hard to read.