Can we create a single Notification with data from multiple records?

The short answer is that this is not possible without also using Custom Events and Escalations.

The Notification functionality is intended to provide information about changes to a single record at a time. In order to accomplish the effect of a single Notification sending out data from multiple records, the User would first have to set up a Custom Event that is capable of querying for the desired records. Using the application's Notifications isn't an option because we don't have the ability to loop over an unknown number of child records when Hash Variables are replaced with real values. This would require a much more complex system for constructing Notifications, and Escalation Criteria than is currently implemented. Once a Custom Event exists, the Escalation process can be used to create Criteria that will help determine when the Notification would be sent out. Even using these systems, the content of the Notification has to be built within the Event code. You can't use Notifications as provided by the application.

Contact PCR for assistance with creating these processes using report writing hours.