If you fly a plane along the back of power curve, with increasing AoA, increasing drag and sink rate, when can the plane be said to have stalled? Especially when dirty, flow separation might say little. The airflow might be able to follow the topside of the main wing, but then be unable to turn along the flap upper surface and separate at that point. Or the airflow might be separated and turbulent at wing roots, yet attached to wingtips... which is desired and sought by means like wingtip washout.
Surely stall speed is something which applies to the whole airframe, in total?