David Anderson referred to a BLOG by Tom Evslin in which "done" was mentioned.
"What does done look like" is the core process of the Integrated Master Plan / Integrated Master Schedule (IMP/IMS) used in aerospace. Add to IMP/IMS Technical Performance Measures and you've got "done." Tom's discussion was around how to speak to software developers. The language gaps between done and almost done also exists in propulsion, structures, systems engineering, and other disciplines.
Technical Performance Measures is an approach to managing complex programs consisting many times of "systems of systems," but also of simpler systems. It's out of scope for now, only that Evslin's BLOG is worth looking at for this and other information. And importantly that TPM's IMP/IMS and other "done" defining processes are standard fare in domains outside software development.
There is closure between APM and existing processes, I just know it.