I purchased a student version in Jan 2019 for a CAD class. it ended in May. I drew some stuff up for a class today while in class. Took it home to work on it and my student version 2018 bought in JAN 2019 won't let me open it. to work on it away from school. It's not cool.
What message do you get? Or do the files just do not open? Without any other information, my guess is the files you brought home are a future version. No backward compatibility ever.