I'm having the same issue. I could swear that Turnitin used to allow resubmissions up to the deadline; I think it was even an option that we could select, and I always selected it. Now, I don't see the option anymore. I agree that it's very cumbersome to have students contact me, then I have to manually delete the original submission. It's especially bad because there's always the chance that the student didn't actually want it deleted or won't be able to resubmit, and I could accidentally delete the wrong student's submission. There's just too much potential for human error. Please give back students' ability to resubmit!