I do know the feel. I was young once (seems a long long time ago). Reinventing the wheel was fun and challenging. I loved creating libraries. I didn’t actually know at the time that there were already existing libraries I could just use, this was the 90s. But it is hard to keep track of what library code exists in a project if you didn’t write it. Maybe assign them to review the library code and document it or something. Then they will know what it is at least.