Most planes have 2 electric trim switches per yoke as a safety measure as one completes the circuit, activating the system, whereas the other controls the motor to activate the trim. Plus, its also required by regulations (as far as I remember).
So my questions are: Why did the Airbus A300/A310 series only have a single trim-switch per yoke? Was this the result of a more advanced design choice for its era? If so, why wasn’t this feature used on any other aircraft that came later on?
An Airbus A310's trim switch
A Boeing trim switch