In many processes, assumptions are made and information is stored in advance of hard facts or the actual event/instance. Afterwards, revision of the data may be flawed, overlooked or not deemed worthwhile. In such circumstances, information can be inaccurate or may have been left out.
An example is names of people attending a seminar. An atendee preregisters himself and one additional colleague, to-be-determined. At the seminar organizers may or may not capture the actual name into their system. A registration sytem might be designed in many different ways to handle this use case.