Final answer:
The use of 'AND' signifies separate contributions while '&' indicates a collaborative writing effort by the screenwriters, according to screenwriting credit conventions.
Step-by-step explanation:
In the context of a screenwriting credit title, the use of 'AND' between Matt Charman's name and Ethan Coen's name, but an '&' between Ethan Coen's name and Joel Coen's name, signifies that Matt Charman worked on the screenplay separately, while Ethan Coen and Joel Coen worked as a writing team.
This is a standard formatting convention in screenwriting credits. When you see AND between two names, it indicates that those writers worked on the screenplay at different times or drafts independently of each other. On the other hand, '&' signifies a writing partnership where the writers collaborated on the screenplay together during the same writing phase.