The communists would have us believe that the working man, or "labor" is the man who lifts heavy objects or digs the ditch with the strength of his hands.
They do not believe that a man like Donald Trump, for example, through is machinations, while not of the physical type, creates things. When the Donald is all said and done, there stands a towering skyscraper where nothing existed before it. This in turn enables the effort of others and provides for them, both during and after it's creation.
This, I think, is a small illustration of the non-static nature of labor/capital which you describe and the Marxists refuse to acknowledge.
The hilarious thing about that is while the grad-school marxists claim to "dearly love" the laborers, in real life, they disdain and hate those who work physical jobs. They look down upon physical laborers, unlike Conservatives who believe that there is virtue in all work.
Mark