Hope this makes sense.
My original terminology was a little misleading - instead of being 'Historic' calls the reporting was actually meant to show incidents with custom statuses, which were set to be class: Closed in order to keep them seperate from day-to-day incidents. Our management requested these still be logged in the system but not show up in the dashboard views by default (or the main Service Request view. The easiest way at the time seemed to be setting them to be 'Closed' instead of 'Open', which allowed us to view them if required, but did not show them by default in the other views or the main Service Request view.
Because of this, the 'Active Service Requests' report in Design Dashboard was unable to see these statuses, and we were unable to create a graph on these requests. If we changed them to Class: Open, our main Service Request view was clogged up by a lot of non-critical Report & Training requests.
Instead of trying to get the dashboard to show a custom report on these statuses, I changed them all to be Class: Open, and then applied a new filter to the main Service request view:
List Field: status
Lookup table: cust_values where list_name = 'status'
Lookup filed: *blank*
Lookup caption: value_caption
Lookup key: value_key
Filter Items: Incident: (status = 1 or status = 2 or status = 3 or status = 4 or status = 5 or status = 6 or status = 7)
Filter Items: Training (status = 14 or status = 15 or status = 16 or status = 17 or status = 18 or status = 19 or status = 20)
Filter Items: Report: (status = 35 or status = 36 or status = 37 or status = 3
By default, the Service Request view filters on 'Incident', which displays exactly the same incidents as it did previously. We can now filter and show all Training or Report requests from the same view, which has actually improved operation of the queue (previously we had to filter specifically for 'Status: Report Request Open', 'Report Request In Progress' etc, and couldn't see ALL report request statuses in one screen)
Back to the Design Dashboard, now that all the statuses are shown as Class: Open, the 'Active Service Requests' report can see them all. I've created several new views, filtering on Status Indidents: (Status = New Or Status = Open Or Status = Pending Or Status = Postponed)
Reports: (Status = Report Request Open Or Status = Report Request Scheduled Or Status = Report Request In Progress)
Now we have several Speedometer graphs, one for each of our incident types, and three seperate views of the main Service Request view.
In hindsight, this would have been a much better way of setting up the custom statuses to begin with, but it took a request for multiple dashboard views to make me realise it.