Mastery implies continuous improvement, commitment, seeking perfection as perceptions and values change. I found this description of "personal mastery": "Personal mastery is a set of specific principles and practices that enables a person to learn, create a personal vision, and view the world objectively". See: http://study.com/academy/lesson/pers...ples-quiz.html
. Unique to each individual, not a declared level.
Expert is more high level of skill and understanding, a level for the few, not the many. Expert doesn't imply continuous improvement or change.