Unfortunately, every insurance company and the government will all administer these rules differently.
It is impossible to know how specific to be in many cases, especially if we are coding for symptoms and don't really have a diagnosis.
In reality, we will each build our own library of accepted codes based on our individual experiences with the insurance companies we bill -- it will only take a few rejected claims to figure out which claims get paid.
As I said a long time ago, ICD-10 is not at all about increasing the accuracy of coding (for some not-very-well-defined public purpose that "demanded" ICD-10). It is about jobs for coders, coding teachers, conference centers that host "coding workshops" and revenue for the AMA selling code books.
Real doctors will learn to game this, and very quickly.
