The guys from DrinkBox Studios have recently published the first pitch video from their current game Severed that was sent around internally after they finished their last game. That’s also an example for a huge leap from concept/idea to finished product.
Pitch: https://www.youtube.com/watch?v=KmFWw3ooDk4
Release Trailer: https://www.youtube.com/watch?v=CIP35f_SbPI