Rainboe - you are confused by the meteorology you learnt all those decades ago. It is true that at temperatures below -40, the amount of water vapour that can be held in air is so small as to render super-cooled droplets irrelevant, and that is the basis for the existing guidance. HOWEVER, in conditions of strong convective or lenticular activity, sc droplets can be carried aloft into temperatures well below -40. Ice crystals are also a threat to engines at those temperatures as you should have read on these very forums. Things HAVE changed. You will do what you are used to over '40 years', of course. Others take note of new information and learn. Out of interest, what do you see as the problem in using anti-ice in relevant high-level cloud at temperatures below -40, apart from a very small fuel penalty and the fact that you will no doubt have noticed over the years that the 'bible' does not say you should not use it?