Even if we consider everything else to be correct in above assumption ( well, that is still a big IF), there is still one big assumption to be considered in this "model". I think in may-14 at least, the number of application received by CIC would be high in first week. This would be those people whose package got returned under FSW-2014 and they were always ready for FSW-2014.
However, from 2nd week onwards, mostly non FSW-2013 would have started sending their applications. These are those people who would have "mostly" started ECA/IELTS after FSW - 2014 announcement.
Hence, "average" assumption made above is mostly skewed due to first week may-data and bound to give pessimistic outcome.