Takeoff flaps is the key to this. That might mean flaps up or not up. Vmc has to be above stalling speed. If not, there is really no Vmc(a). I believe the B-N Islander falls into this category and of course the C-336/337, for obvious reasons.
Keeping in mind the conditions and aircraft configuration established for measuring Vmc published in the certification requirements, actual Vmc can be at a higher airspeed given the higher DA, lower power, higher temp, lower pressure, CG, etc. Vmc can also be at a lower airspeed at a lower DA, very cold temp, etc.
In doing an unplanned Vmc demo in the Twin Otter simulator, exceeding the 50# torque limit will result in a higher demonstrated Vmc and loss of directional control, which is why there is a 50# torque limit when upgrading the engines from -27's to -34's. Vmc in the Twin Otter is with flaps 10, not up, BTW.