Meanwhile, the Royce paper that takes down the simplistic series of steps arranged in a waterfall, is a sort of formalization of an approach better visualized in late 80s as "the spiral model":
The concept of both, well before the 90s, is you don't know what you don't know, so its faster and more successful and costs less to make, learn, and document from prototypes before you know, to establish what you're really making.
If you want to see a valid method "back in the 90s", see DSDM:
https://en.wikipedia.org/wiki/Dynamic_systems_development_me...
Meanwhile, the Royce paper that takes down the simplistic series of steps arranged in a waterfall, is a sort of formalization of an approach better visualized in late 80s as "the spiral model":
https://en.wikipedia.org/wiki/Spiral_model
The concept of both, well before the 90s, is you don't know what you don't know, so its faster and more successful and costs less to make, learn, and document from prototypes before you know, to establish what you're really making.