The script from the art of star wars isn't actually the 4th draft as it was written. it was taken from one of the later cuts of the films, when the biggs scenes were still in. You'll probably find that the script on IMSDb was copied from the art of star wars. It's pretty obvious when you watch the film that it was not filmed the way it is in the art of star wars script, but was filmed the way the 4th draft of march 15th 1976.

http://starwarz.com/starkiller/star-wars-the-adventures-of-luke-starkiller-revised-fourth-draft/