Hi
some mistakes about anti ice on 737 or misunderstanding.
1- WAI and/or E/I work slats extended, but not on the flaps of course, not on the elevator and others parts of the airplane. That the reason why, it's not recommended to hold at "low speed" in icing conditions.
2- Vref ice : if WAI was used during flight, is only due because the computed Stall warning logic adjusts stick shaker and minimum manoeuvre speed bars on the airspeed indicator on the NG.
But on the CL, Boeing says in App and Landing :If ice formation are observed on the airplane surfaces, VREF ADD 10kts this ensure maneuvering capability. Not the same logic.