Not all playwrights do research. A lot don’t have to: they are writing from the hip, creating their own worlds with their own rules; or they feed off of their own histories; or they are genius historians who just have the knowledge in their brain.
But some playwrights do research and you can often tell when they did. And as a dramaturg you find that there is a point where their research stopped: a point where they decided they had enough facts to create a believable vision of a time period or an occupation or a specific situation. A research horizon.
The question for the dramaturg is: do I stop? Does it benefit anyone to understand the reality of the play’s world better than the playwright herself? Sure it is self-gratifying to say, “Oh well, this writer obviously didn’t understand the historical significance of the racial tensions behind Eeny, Meeny, Miny, Moe” but how does this back-patting help the production? And what research was sacrificed as the dramaturg unearthed this tidbit?
Research is endless; we choose our battles and rarely win them.