When we use derated (10% or 20%) power as determined by our performance software by itself or in combination with an assumed temperature method (reduced thrust takeoff), Vmcg and Vmca are computed using maximum derated thrust. So, in those situations (such as the one Purpletoolbox described above), we don’t have assurance of full control authority should we select full rated thrust. The flight manual cautions that a thrust increase during a derated takeoff following an engine failure could result in loss of control. In fact, Boeing recommends not advancing the throttles during an engine out when using the combined derate and assumed temp because the derated max limit the Vmcg and Vmca is based on is not displayed.