We just added Original Deadline as an optional column (hidden by default) in General Report. It allows you to easily detect what projects/tasks missed the deadline. This field is also included into CSV/Excel export.
About Original Deadline. When a project or a task is closed (marked as Done) its deadline becomes the real close date. If the closure date is different from the deadline that was set for that project/task (and if it is present) then this old deadline is saved into Original Deadline. So if a task was supposed to be closed on May 10th, but was closed on May 15th, the Original Deadline will show May 10 and the Deadline will show May 15. You can display Original Deadline besides Deadline in main view or General Report to easily detect missed deadlines or to compare those two dates.