The dance music used for the ball scene included Michael Turner's waltz, credited as Mr turner's waltz in the end credits (nothing about Mendlesson for that one).
The other folk tunes were used as scene setters partly to indicate passage of time.
One of the secondary charaster is a farmer, who would have not moved in the same circles as the main characters so it could be said that more rural folk music was appropriate for him.

There was a trailer for the forthcoming production of "The Secret Garden" which seemed t show a 1950s railway carriage!

Robin