When a new event has been created or an existing event has been edited, notifications are sent to all subscribers automatically.
For Public Calendars
When changes have been made for the public calendar, subscribers of the public calendar will receive messages in their inbox as well as a red circle on the public calendar.
For Public Events
When changes have been made to the public event's description, date and time, and location, people who have added the event to their calendars will have the event updated automatically from their shared/personal calendars.