What's the difference between "and" and "&" in movie credits?

Question

I recall hearing once that there was a difference (due to guild rules) between the use of "and" and "&" when discussing collaborations. For example, a film that has

Screenplay by Bob Loblaw and Dr. Dre

means that the writing was divided differently than

Screenplay by Abraham Lincoln & Bobcat Goldthwait

which is different again from one that says

Screenplay by Alan Smithee and Trogdar the Burninator & Guy Ritchie

What are the rules, and is it consistent amongst the guilds? I.e, do Director collaborations also have the same semantics?

Answer 1

Found a couple of references although different countries may have different guidelines

Source A - US Rules

The ampersand (e.g. “Al Gough & Miles Millar”) means that the two writers are a team, and are treated as one person for WGA purposes.

The other version (e.g. “Josh Friedman and David Koepp”) indicates that the writers worked at different times. In this case, the screen credits manual says…

The order of writers’ names in a shared credit may be arbitrated. Generally, the most substantial contributor is entitled to first position credit. Where there is no agreement among the arbiters as to order of names, or where the Arbitration Committee determines that the credited writers’ contribution is equal, then the Arbitration Committee shall order the writers’ names chronologically.

Source B - Writers Guild of America

What is the difference between the word “and” and the ampersand (“&”) located between writers' names in a writing credit?

The word “and” designates that the writers wrote separately and an ampersand (“&”) denotes a writing team.

Answer 2

What are the rules, and is it consistent amongst the guilds? ie, do Director collaborations also use the same nomenclature?

In general, the Directors Guild of America (DGA) has a "one director rule" that prohibits multiple directors receiving credit on a film. Exceptions are made for established teams who share a creative vision (like the Coen Brothers, the Wachowskis, Phil Lord & Chris Miller, etc.). In the case of Lord & Miller, they are credited (on The Lego Movie, for instance) with an ampersand instead of spelling it out, which seems to support the same kind of interpretation that the Writers Guild uses. But that is just one example and may not be definitive.