These conditions are apparently very rare and elusive
Perhaps not as uncommon as you think. I just did a sim today and one of the discussion items was on "Ice Crystal Icing" (Boeing QRH title), the check captain said that there had been one or two occasions of it happening a month. Yes I know that amount of events is minuscule compared to the amount of GE engined aircraft that fly every day, but I wouldn't want to be there when it was happening.