Marcel Breuer Wassily Chairs by Knoll or Stendig?  

I just bought these chairs online, but do not have them in hand yet, so I can only show the pics they shared for the sale.
I assume more detailed examination and pictures will be needed to authenticate anything - the site listed them as "Manufactured by either Stendig or Knoll, unsure which one." Not to sure about that but the price was right so I bit.
Before I try and see when/weher they were made, I was curious about the gray straps. I had a real hard time finding any information on older versions, or very few pictures online of this color. Does that lead me to any conclusions related to make or timeframe?
Just curious.
If you do see anything from these pics that is informative, please share. Thanks!