Interesting. However, the different behaviour in the cold or when first running may be due to other factors presumably? Not just another year's mileage, but presumably you have had the car serviced in the last 12 months, so new filters etc?
We had the car last serviced in December and started using V Power in March this year; between that period it was still behaving in the same way as it did from new.
For that reason I do genuinely believe that the improvements stated are down to the change in fuel. It seems too much of a coincidence otherwise.
However it's not out of the question that it just "sorted itself out" - it is a Fiat after all!