Great thread that goes back quite a ways. The problem with these want-to-know questions is there's not a thorough source of info. I worked on two James Cameron films, Abyss and Aliens. I sculpted both full-size mini subs by myself from Ron Cobbs' blueprints. I spent hours going over them because the dimension were off in a number of places. If I had just started sculpting, nothing would fit. I'm pretty sure they changed them after I marked them up. Everything you see on those subs was sculpted in an airport hanger in Van Nuys on the hottest month ever in LA, over 100 f. The Canadian subs didn't arrive until after I sculpted everything around them. I called the company to make sure their dimensions were correct and hoped for the best.
Then, a few months later, in winter, a few sculptors and I sculpted all the interior tunnels for the spaceship. It was so cold, it snowed where we were (which never happens in LA), and there was no heat in a wooden garage. The producers gave zero ***** and I got zero credit. Maybe Cinefex gave me credit since my sculptures are on two of their covers: the mini-sub and the Beetlejuice snake that I sculpted. I didn't get a credit for that film either. So, being in the sculptors union (which is the smallest union in America with 40+ people) gave us zero power and they didn't look out for us. All it did was allow us to work on union films.