Hey there Norman 
Basically, Scanias L113s and ELBOs are not considered rare on
Service 921, because it's permanent bus' a Scania itself - TIB638T.
What I considered rare is the deployment of MBO.405s and MB
Volgrens on Service 921.
For Service 920, I dont think any of the buses deployed on it's
rare, though Scania ELBOs could be considered, because sometimes
Scanias can be seen on Service 920 already. But then Nissans are
really rare, just like those deployed on Service 970... Though I
dont think it'll be any longer rare for Service 970 to have Nissans
deployed 
