This was a class 'discussion' item last nite.
Vd is a fpn (Fine Print Note), not 'Code' not mandatory.
Vd is a design issue, and could/may be debated via 110.3 (B)
'Good Practice' & 'Common Sense' are not in the NEC, but should be observed by all.
I would check the equipment for a voltage, and take a reading under load, if it's already installed. Or, I would do the calcs on paper beforehand, and 'lean' to a larger conductor.