Assignment Scores page dluplicates if students are not assigned at the same time

Maybe this can be easily resolved at the assigning stage, but I've not seen it. So, if I assign something to a class, but another student comes a day later, unfortunately I cannot simply add this individual to an already assigned assignment, so I assign it separately and it shows up separately. Either make it easier if I'm missing something, because I've missed it for years, or make it so adding other to an assignment (even if the due date will be later for them) so that I don't have a mess of a Scores page later.