when the vmcg and vmca is truly recalculated due to the choosen derating on a 777 it may make sense that you indeed cannot restore maximum underated power in this case.
that would be absolutely new for me, at no airplane i drove it was that case but when it indeed is so at this plane it would make sense.
but what for (single engine) perfomnace tables? do you have three complete sets for 90B TO1 and TO2?
interesting!