Two more points about movie credits. One is that as a couple of correspondents noted, many animated features are not covered by the WGA and some of them have been known to either list many writers or to credit someone as writer who, rumor has it, never wrote anything. This whole business of the Writers Guild covering screen credits came out of a time in Hollywood history when studio execs would sometimes put their own names, or the name of a relative or favored writer on a movie that was actually written by someone else. There were stars who would write nothing but demand and get the screenplay credit. Mae West would even go so far as to give interviews where she talked about how she had to write her own scripts because there were no good writers around. Anyway, this still goes on with non-WGA movies, both live-action and animated.
The other point: As I mentioned, the WGA erupts in Civil War every time someone proposes changing the way screen credits work. One root cause of the friction is that different folks want credits to do different things. Some want the credit rules to influence how the business works. Others want credits to merely reflect reality. The first group believes that it would be great if less rewriting went on, even if it leads to less employment. So to make rewriting another writer's script less attractive, let's make it harder for rewriters to get any credit and impossible for nineteen guys to all get credit. On the other hand, the second group would argue that main goal is that the credits should be accurate. If eleven people did contribute to the script, that's what the credits should say. Obviously, credits cannot do both. They cannot be denied in order to discourage rewriting but still be awarded to all the rewriters. A further source of conflict is that many of the residual payments on a movie are linked to the final screen credit so a guy who's going to get his name on the film has a financial incentive for keeping the names of others off.
I've long thought that if the Guild is ever going to solve this conflict, they should start by having the membership vote on a referendum: Which is more important? That credits reflect reality or that they promote the notion that movies can and maybe should be written by one or two people? And then a committee could try to revamp the rules in accord with the wish of the majority. The only problem with this is that I'm not sure how I'd vote.