Our thrust display shows the fixed derate, IE the vmcg/vmca protected full debated thrust if you will.
If performing a combined derate and assumed temp take-off, advancing the thrust lever to the fixed derate shown on the N1 reference bugs is permitted (however should not be necessary).
If performing a fixed derate take-off advancing the thrust past the fixed value is not recommended but may be accomplished if terrain contact is imminent. Doing so may result in loss of directional control.
I believe what they are getting at is vmca rather than vmcg but I may be wrong. Worst case vmcg is 106 kts, if you are above that you are fine regardless of conditions on the ground. In flight I'm not sure but maybe there are vmca tables out there?