Of course production has to start early to meet the demands before it actually go on sale. Canon wouldn't announce a camera for distribution on a certain date and show nothing for it. And they also have to provide sample cameras to the photographic communities for evaluation.
The demand is probably quite high during the initial sale period. I don't know how many 5D's are being made pr month but I saw that someone estimated 30.000 D800 being made per month (and 5.000 D4's). Link:
http://www.techradar.com/news/photography-video-capture/cameras/nikon-reveals-d800-production-targets-1063413
Does anyone know how many D5 mk II's there have been made? Or 7D or D60 or Nikon D700 or well something to compare these numbers with?
My guess is that 'a lot of people' have preordered and a lot of people will order as soon as the first people are getting theirs (friends who see it, people waiting for reviews etc). But does anyone have numbers for how many these 'lot of people' usually are? Is it the same amount who would buy the camera during 1 month, 6 month, a whole year???