Sometimes an Event will be announced as slated to occur on a given date at a given place at a given time, then it will be postponed for whatever reason. Currently we have no guideline to cover this situation. There are two options to deal with the situation: just add the Event that took place with an annotation about where and when it was originally supposed to take place, or add the original event's details, mark it as Cancelled, and link it back to the event that took place (via an annotation for now; it may be possible to add a relationship type for this later).