Dictionaries report common usage. The migration of common usage is often the product of the philosophy/culture dominant at any given time. When a philosopher like Rand overturns the common philosophy, it results in a new and different understanding of a multitude of concepts and their relationships.
Sometimes a concept or a context will be different enough to require a new word like psycho-epistemology. Sometimes it requires disambiguation by separating two words that have lapsed into having one meaning, like duty/obligation. And sometimes it requires discarding a meaning that is self-contradictory or otherwise not logically viable and replacing it (or adding another context for it) with a viable meaning, as Rand did with selfishness.
In a discussion such as ours, the words and definitions are a means to the end of communicating the concepts. The meat of the discussion is only the latter. In this case the alternate concepts of chosen v. unchosen moral imperatives stand untouched by your complaint that Rand's use of duty does not comply with common usage of the word. And, speaking of new words, Rand maintains the word "duty" is an anti-concept: an artificial, unnecessary and rationally unusable term designed to replace and obliterate some legitimate concept. “Duty” — Ayn Rand Lexicon
Ultimately, if we do not reach agreement on the symbols of these concepts, as Rand uses them, you are free to signify these concepts with different words and I will create a foreign language dictionary so I can translate your words into mine.