Solution
The NI 9470 does not require external flyback diodes nor does it contain discrete built-in ones because the protection is integrated into the output stage architecture.
The NI 9470 output stage consists of a switching half-bridge of MOSFETs that always drives the output with low impedance by connecting the DO+ end of the coil to either VSUP or GND. Because there is no interruption of current flow to the inductive load, a flyback event is prevented. In the event of an unlikely discharge, the internal body diodes of the MOSFETs provide a safe path for a flyback current.