What is the significance of the date 1787?

The Constitutional Convention of 1787 was a conference held in Philadelphia in which state delegates met to frame the United States Constitution. The purpose of the convention was to amend the inefficient Articles of Confederation that had served as the preliminary constitution for the United States since 1781.

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.