Premise: no one is required to do anything.
At any point we may say this is not a priority and everyone goes home.
The software shall exist in whatever state we choose to leave it, even a non-existent state.
Corollary: no software is required to exist.
Priority is chosen. As soon as priority is required, we enter the realm of policy:
The software shall exist.
The software shall be functional.
The software shall be good.