One of the hardest things about writing historical fiction is being accurate to the details. 
That is true. It would be hard to have every detail
I think one of the most important parts is the social conditions and manners of the time.
Yes things were quite different than today
Etiquette has definitely evolved over the years. 
It is not valued as highly today in my opinion.
Very true. In historical times etiquette was so important which can make it hard to write without daily experience with it. 
Today's children are not even taught etiquette the way children once were.
No they aren't. I'm not sure many even know who Emily Post is anymore. 
Perhaps our world would be quite different if everyone practiced more etiquette in their every day lives.