It bugs me I really wish they would would tweak those categories to include a "probably carb ice" if it looks like a duck and quacks like a duck... Unexpected power loss, wx favorable to icing - no other visible cause... Call it probable icing.It fits the scenario that by the time the investigator gets around to opening the cowl and checking things out, the ice has melted. So, another "unexplained" loss of power.
The fact that the traditional aero engines are double the icing rate of the others says it all. We see the attitude here regularly "I live in the south it won't happen, I don't need carb heat"