I've been impressed with these period pieces, mainly because the authors' are doing their homework. By this I mean research. They have been researching the costumes of the day, the common language used, backgrounds--common homes, history of their time period--politics--and so on. Another important factor is to use names that dominated your period. This includes first and last names for both men and women.
One novice writer sent me the first 18 chapters of a piece written around the times of the 1700's. She mentioned the hardships that most people faced, including the scare job markets, along with poverty and starvation. Her plot covered a traveling circus run by two men and a women who did what they could to survive. The names she chose were fantastic, along with common foods eaten during that period, and what the circus threesome did to survive. Most of the acts they performed were extremely dangerous, and cost one male member his life.
Then came the question of a religious burial, which they couldn't afford. How the remaining two solved that problem through a devastating decision ended the 18th chapter. I'm still waiting for the remainder of that novel since it was an emotional page turner.
What I'm trying to say is this: I viewed a picture about the old west one time and was shocked to see a cowboy wearing an expensive, modern day watch. Was the director consciously aware of the mistake? I've also viewed period pieces that had characters speaking modern day slang--"Are you kiddin' or what?"
These sort of flubs can cost rejections when it comes to publishers, movie companies, and whatever venue you're seeking, The answer is research and lots of it. Of course, for all of the research you perform you might not be able to use all of it. If you've done say 60 pages of research, sometimes you can only use ten pages of it, lest you cram your novel with too much research, causing a drag in the flow of your novel.
Writing a period piece isn't easy. However, the fact remains that all novels--whether period pieces or not--require research. You just can't stick facts in because you imagine they fit. You must be 100% positive that your facts are real.