The date that is displayed on the overview block for the action events isn't always the same for all activities of the same type. For example, in activities that have an available from and available to date we will use the available to date, if it's set, otherwise we'll use the from date.
This means that sometimes the date refers to when the activity opens and other times it refers to when the activity closes. It would be good to indicate visually which of the two the date is representing for that event so that users don't accidentally think a closing date is an opening date.
See scorm for an example of the availability dates.