public DiagramLayerConsistencyState ConsistencyState {get;}

public void GetDiagram(DiagramLayer diagramLayer)
{
  // note - methods need to run on MCT

  NetworkDiagram diagram = diagramLayer.GetNetworkDiagram();

  // get the consistency state from the layer
  DiagramLayerConsistencyState dlState = diagramLayer.ConsistencyState;

  // or from the diagram
  NetworkDiagramConsistencyState ndState = diagram.GetConsistencyState();
}