I'll add another perspective, here. I am a graduate student and former high school teacher. I would never expect a student, even a student in university or graduate school, to turn in an electronic copy after they had already given me a print copy. I find such a request extremely irresponsible at this level. As a high school teacher, I once misplaced a student's assignment. I felt terrible and it caused me a lot of anxiety; thankfully, I found it. I have taken great care to never repeat that mistake. Even at the university level, why should students have to do extra work due to an instructor's mistake? That said, such problems could be avoided simply by requiring all students to turn in electronic copies rather than print copies.