In case of using A for buffer layer,3 different materials are possible to be mixed at edge portion which is close to base die. 1 layer deposit of No.12 is easy to be diluted by 2 other base materials.
Therefore, substantiail properties of No.12 are to be changed and is not able to keep wear reaiatance. Or, No.12 is itself aroud 44-52HRC hardness and does not have enough ductility for stamping.