Possible duplicate faces (zero faces)
At 4:50 where you start to push in that top ridge, I was getting duplicate faces layered between the faces. I'm sorry, I've already deleted them all (hopefully it doesn't screw something up - doesn't appear to yet).
Is this something to get overly excited about?
EDIT: Uggg... it would appear that getting rid of those faces was NOT the answer as it now breaks adding edge loops to those areas. I should have waited until you got farther in the video where you noticed a 'seam' where some vertices weren't close enough together to remove doubles earlier. Another hard lesson learned.
EDIT: Luckily was able to backtrack enough and increase the merge distance enough to capture them all