I’ve always felt vaguely sorry for 4th Avenue. As anyone familiar with Manhattan knows, it’s a pitiful little road, stretching a mere 7 blocks between Astor and Union Squares. However, in literature on pre-War NY, I’ve read references to it stretching up further north, up to the 20’s, 30’s and even 40’s. Was what we now know as Park Avenue South once considered 4th? Was all of Park Ave? And if so, when - and why - was the change?
It was originally the Bowery (farm) Road. Later Fourth and then Park Avenue. The section called Park Avenue South was renamed in 1959. Since they only renamed sections of the avenue each time it still has all four names depending on the cross street.
http://www.thecityreview.com/parkave.html
http://www.forgotten-ny.com/streetnecrology/AveA/declassified.html