Narumama quotes John Lennon's line "Life is what happens to you when you are busy making other plans". Although the film is set in 1975-76, the song Beautiful Boy from which this line is quoted, was released only in 1980.
The place (surya's building) where all the friends gather and tease passersby you can see a window with a scenic view exactly before Mukund and Surya are talking about "sakhardande", but later when they are leaving for school, one can clearly see a green screen that is used for special effects.
Film is set in 1975.For a scene there is Kimi Katkar's named mentioned who had started working in mi d80s in Hindi films.