When Miriam dances with Joel after accepting his proposal, the street is wet with rain. However, by one of the cars you can see that the street is dry, indicating that the production sprayed the street with water, a common tactic in films and TV since it makes pavement look more dynamic on film.
When Midge startles Susie by dropping in unannounced, Susie says she needs a defibrillator. In 1960s, external defibrillators were only used in hospitals, and were largely unknown to the public at large. It wasn't until 1972, with the introduction of the TV show "Emergency" that knowledge of external defibrillators became part of popular culture.
The address given for wealthy Sophie Lennon's townhouse mansion on Manhattan's East 98th St would put it either in the middle of the East River or in the middle of a subsidized housing project, certainly today but especially back in 1959.