The fact that somebody benefited from the output of your work is not the same thing as extracting your labor. Extracting your labor means that before you even create the work, they're conscripting you to do it.

For example, I created a useful organization at my school before I graduated. That was twenty years ago. It still exists, and people are still benefiting from it. But they don't somehow owe me compensation, nor would I go around saying that they're somehow exploiting me or expropriating my labor just because they're benefiting from what I've done in the past.