Servicedesk NMS Integration is creating new incidents for every event (which is set as a Bad Event in NetworkManager Configuration in Console) that is picked up from the NMS database. Events for the same device are creating new incidents rather than updating the existing incident for the device and Good events are not resolving the incident.
In NetworkManager Configuration in Console, the NMS Reference was set to a unique value for each event (i.e. Id). The Network Integration service uses this reference (which is appended to by the Event Group) to identify an existing Incident and if this is different on each event, it will never identify the original incident that was logged. Setting this to be 'Map Id' (which is a unique id for each device) in this case, resolved the problem. If no Incident with that Map Id exists, it will create a new one for the specified Bad events. If it exists already, any specified Bad events will update the Incident and specified Good events will resolve the Incident.