Let me rephrase that: No, we didn't do any manual undervolting, what MSI Afterburner does "behind the curtains" automatically is a different thing.Note that on Pascal cards, at least vith MSI afterburner, overcklocking also implies some form of undervolting.
Afterbuner deals with a voltage / frequency graph. + 50 Mhz is equivalent to increasing the frequency by 50 on _all_ the voltage steps. Hence after +50 is applied, the card will try to achieve say 1600 mhz using the voltage that was previously required for 1550 mhz. (if it fits in the power limit).