I graduated from university in June of 2015. I submitted an essay to a philosophy professor in my second year that was substantially the same as an essay I submitted to a TA the year before for one of the the same professor's first year classes.
I wanted to use my research and essay content for the second year course because I was enthusiastic about that topic and wanted to use it again. I asked the professor if I could use textbooks and information/material studied from his first year course (which also wasn't a prerequisite for the second year course) and he said that was fine. I wasn't really aware of this "self-plagiarism" rule back then and I figured he was saying it would be fine to use the content of my old work from the previous year as well. I do remember changing some parts of the essay but the two had substantially the same gist and body.
I just realized recently that I need written permission from the professor in those situations.
Theoretically, if they could prove now that I committed some sort of academic misconduct for that back in my second year, (2013-2014, I've had my four year honours degree since June 2015 and am now working in my field) what would the penalties be? Would my degree be revoked and would I be required to take another course? Would they just adjust my course or assignment mark?
I know it depends on the circumstances so I broke it down and let me know if there are any more details you need to know.