You mistook a Cardinal for a DASH8/ATR???? As the former lead FTE on one of the DASH8 flight test aircraft I should take the hump at you misidentifying my pride & joy!
As for placarding on the quadrant, you will find that FAR/JAR Pt25 is fairly strict on what labels are used for each position on the condition levers.
As for going into the ground beta range while in flight. Yes it has been done before on the larger commuter aircraft and a few engines have been oversped as a result! The gate to go from flight range to grond range requires lifting "triggers" to allow the levers to move further aft. Therefore, pilot action is required to go behind the "gate" so you can surmise how these in flight occurrences occurred!!
It should be reassuring to know that the authroities are now pushing beta lock-outs that will prevent selecting levers behind the gate in flight.
As for airbrakes; all comments about the big egg beaters being good airbrakes are perfectly true!
If you want to be a really techno whizz, you dont actually need condition levers. Through the wonders of FADEC and PEC (propeller electronic control) the balde angle is automatically controlled by the PEC while the FADEC sorts out the torque.
Hope this answers the question.