because this has a little to do with setting, creative limitation and genre, I am going to talk about AUTHENTIC here.
To my mind, this is one of the most important parts of the whole McKee book. It was a revelation when I read it. An author means authority and that results in authenticity. The reader is willing to suspend disbelief because she is totally absorbed in the world that the author has created.
The writer knows everything about the world she has created. The important words are: the world she has created.
In the author's world she is God. No sparrow falls without her knowing why. It is not the entire world. There are far too many unknowable imponderables. The world an author creates is never 100% accurate. The author needs to always choose what to include and what to exclude. It is at best a reflection from a Claude glass. Claude glasses were popular in Regency and Victorian times among painters and tourists -- people who wanted to smooth out the ugly and have a certain view of the world. By using different tinted mirrors, the viewer was able to see the scene in different aspects -- fiery, moonlit, in winter etc, without ever having to actually be there. This is what story does -- it holds a smoky mirror up the world.
What happens when an author creates an authentic world is that the reader willingly suspends disbelief. Sometimes, the reader can't details out of her head and goes to check, thus learning more about the time period or the location that the writer has set the story in. This is excellent as the story has touched the reader.
Authors do research so they can decide what to leave in and leave out and to make their world appear more authentic, but they can never be 100% accurate. A historical written in 1957 is very different from a historical set in the same period but written in 2007 and is most certainly different from a contemporary novel written at that time. IE Jane Austen is contemporary, Georgette Heyer is constrained by her own reality just Nicola Cornick or Loretta Chase (to name two of my favourite current Regency authors) are constrained by theirs. I would never mistake them, and I adore them all. And indeed being in the midst of Decency and Disorder --The Age of Cant 1789 -1837 by Ben Wilson, I will never quite look at the Fancy, the Four In Hand or indeed Cambridge University during the period in quite the same way again. It does not mean my enjoyment of the novels is any less as the over riding STORY is what makes them.
Accuracy helps to build authority and authenticity by providing the TELLING DETAIL. It means that when an author does take a leap, go up the wrong way on a one way street, the reader who knows forgives because she is so entranced with the story. It is the preponderance that makes the story, not the specific detail.