This is a very early stage of a study and hasn't been peer reviewed at all yet. I wouldn't put too much hope on it being more accurate than what we have already seen. It has already been debunked by some due to the similarity in the pattern of deaths in this country and others. If it had been around since before Xmas then deaths wouldn't be rising, we'd have already reached the peak.
Everyone that is hospitalised now with the symptoms and those that die are recorded and we can see it increasing daily. We aren't testing more people daily for it, we are testing all those that present. IF it had been around for months then there would be no rise at this time, we would expect to see a similar number each day or a declining number. The fact that we are not means we are still at an early stage.