I had these emails from an old discussion i had with marc laidlaw about 2 years ago, i finally decided to post em here, some info about why we dont have GYFTVS.
"This was from a prerecorded SIGGRAPH demo, I believe, and not a playable engine version. I looked for the footage before leaving Valve to see if I could get permission to release it to the fans. Never got a permission and did not take a copy with me when I left. Sorry!
On Wed, Jul 26 2017"
I couldnt post an image, but this should do.