The naming in OPC UA Part 4 is ambiguous since the term notification is used on two levels.

Most of the definitions in OPC UA Part 4 talk about notification as base concept for a data notification (DataValue + MonitoredItemId) or an event notification (event with event fields + MonitoredItemId).

The number of notifications refers to the number of DataValues and Events in a Publish Response.

See for example the definition in OPC UA Part 4
Table 88 – CreateSubscription Service Parameters
maxNotificationsPerPublish
"The number of notifications per Publish is the sum of monitoredItems in the DataChangeNotification and events in the EventNotificationList."

But Part 4 used the term also in the Publish Response for the structure DataChangeNotification. This is misleading.

The definition in Part 5 needs to be clarified to use similar text like the definition of maxNotificationsPerPublish
"The number of notifications per Publish is the sum of monitoredItems in the DataChangeNotification and events in the EventNotificationList."

Proposed enhanced description:

Table 154 – SubscriptionDiagnosticsDataType Structure

dataChangeNotificationsCount
The number of data change Notifications sent by the subscription.
A data change Notification is one monitoredItem entry in a DataChangeNotification sent in a Publish response.

eventNotificationsCount
The number of Event Notifications sent by the subscription.
An Event Notification is one event entry in a EventNotificationList sent in a Publish response.

notificationsCount
The total number of Notifications sent by the subscription.
This is the sum of dataChangeNotificationsCount and eventNotificationsCount.

Added suggested Clarifications to SubscriptionDiagnosticDataType

Agreed to text edited in telecon.