1. A method, comprising: associating an event template subscription with a particular event subscription, the event template subscription and the particular event subscription both being subscribed to by a same subscriber unit, the event template subscription configured to cause, at least in part, providing a notification to the subscriber unit of availability of input information needed to determine an event state for the particular event subscription; causing, at least in part, transmission of an initial notify message to the subscriber unit with a current availability of the input information; and for a duration of the particular event subscription, upon detecting a change in availability of the input information, causing, at least in part, transmission of an event template notification to the subscriber unit for informing the subscriber unit of the change in the availability of the input information.