I don't believe there's a single word in English that describes this phenomenon. However, it's fairly common in my line of work to consider this a typical property of complex systems such as large software or security projects.
In agile frameworks, the implementation of various features is often an emergent property of the incremental and iterative development process. This is often more effective and visible when using test-first methodologies, and when leveraging agile inspect-and-adapt cycles to their fullest extent.
Because complex systems are complex, it's often difficult to create detailed specifications such as functional requirement specifications (FRS) upfront. In fact, doing so is a known agile anti-pattern. Agile frameworks compensate for this through the use of various techniques that generally boil down to increased collaboration, frequent or continuous integration, tight feedback loops, and incremental scope.
In short, they acknowledge the issue and then work around it by solving knowable problems, rather than the unknown unknowns that fill the funnel of the cone of uncertainty in complex systems. The emergent properties of the system, along with the inspect-and-adapt process, gradually reduce the cone of uncertainty over the life cycle of the project.