There appears to be a post missing.
Somebody described the Q400 system, which suggested that wing and h+v stabs anti-ice were all switched on together.
Or did I dream that post?
If that is the case, then the tail icing would become a red herring. If anti-ice was on, then neither wing or tail should have had ice accretion. For tail icing to occur, a fail signal for the boots should have alerted the crew well before it became a problem? Or - it was not on, and everything iced - hard to believe.
Re: the CVR, the last transmission seems to me to be unprompted, previous comm was a readback with a humorous inflection towards the end, there was no comm from ATC requiring anything from them thereafter.