The concerning the magnetic/electrical properties of the magnetic grades of stainless steel is only with respect to their applications in magnetic devices as core materials.
The stainless is never drawn into a wire and used for winding the solenoid coil or activating coil for the actuator or device. Only copper wire is used for the electromagnetic coil for its high conductivity and the lowest losses.
Stan may have advocated using a magnetic stainless core material for the inductors/transformers as it offers some advantages. But the windings themselves would be copper wire.