Structure in R&H's era shows

So pre-70s shows where always a pending task of mine and only recently started getting to know Rodger's and Hammerstein, Lerner and Loewe etc. and I noticed that certain terms like "I want song", "Exposition song" that are quite prominent in modern musicals do really apply in the kind of formulaic way they do on a Disney musical for instance.

That made me curious about how the traditional book musical works structurally, as I had assumed it evolved onto a fixed coherent form with standard principles. So... Is there a common pattern regarding the position and function of songs on shows from this period? I feel like there usually is a Love Duet and an 11 o'clock number, but the rest seems a bit arbitrary to me.