Cara, this is on another thread somewhere. I believe the consensus was that on some ships there was limited mixing of the classes.
The writer R A Fletcher in Travelling Palaces warns first class passengers against intruding on lower classes. He calls it,"...a shocking exhibition of bad manners and low inquisitiveness."
There's more on this in John Maxstone-Graham's The Only Way to Cross. The bad manners seem to have been commoner in the earlier years.
The movie is not worth worrying about. Rose and Jack did all sorts of things that passengers were not permitted to do. From the flying scene on the bow to the attempted suicide scene on the poop, reality is ignored for the sake of what is jokingly called a plot.
I understand this was a health issue with the U.S. immigration laws in that Third Class passengers could not go into Second Class or First Class areas and Second Class and certainly First Class could not go into Third Class areas ?Are you factoring in U.S. immigration laws?
-- David G. Brown