I've seen some Gantt Software that will show, often with a Dotted line, the actual Closed date next to the Due Date. This is very useful for Productivity Analysis, as you can see how you are tracking with things like loading up too many tasks at once, tasks that have taken too long, etc. I've always thought it was somewhat deceptive for the Gantt to be limited to showing initial Due Dates, as often as a Project progresses, the dates change. Ideally it would be great to see the original Due Date, adjusted Due Date via a Baseline view, and then, ultimately, the Closed Date.