A few gigs ago I joined a BigCo as a part of contractor group to build a new project. The BigCo had a staff member to bootstrap the project and build a prototype which was internally reviewed and approved. When we put our foots on the ground it was already settled that the app will be build with X, Y and Z as the core components.

Two months later that staff member left the BigCo for another organization, and when we found the actual job posting for his position the X, Y and Z were explicitly stated as nice to have for a candidate.

¯\_(ツ)_/¯