Madison Ave Between 51st St and 49th St

The "bus lane to nowhere" that is Madison Ave continues it's inevitable trek northward for today's block. Sure, there's the magnificent back end of St.Patrick's Cathedral and the Villard Houses across the street. But beyond that, there's nothing particularly notable as the street progresses.

One thing that struck me as odd is on the plaque affixed to the Villard Houses; it seems to indicate that it was added in 1975. Yet the historic description refers to events that took place in both 1978 and 1980. Was it assuming these things were going to occur? Was the later parts added after the fact? Am I just mis-reading it?