If I use an auto-grading script and allow students to see their would-be grade based on the auto-grader, is it wrong to change their grades after the due date if I decide to change the auto-grader? I'm curious what others think because on the one hand students could go back and change their submissions as many times as they liked prior to the deadline, and many students took advantage of this to do as well as possible. Now that I've changed the script many students now have a zero (including a few who previously scored perfectly). On the other hand, the issue that these students had was a result of not following an instruction I gave out, which I overlooked while writing the original auto-grader. So is it wrong to change the grades or am I justified?