Skymasters certified for Known Icing conditions

[RRossner]

I have a question pertaining to fully booted Pressurized 337's. Apparently a fully booted airplane with the heated windshield plate is still not officially certified for flight into "known Icing".

My suspicions are probably because the airplane is not equipped with a super heated pitot, fuel vents, and stall warning systems but I’m not sure.

Does anyone know for sure why this is?