Keith, we have reached the limit of your intelligence. Unless you can improve, and quickly, there will be no point carrying on with this.

If you extrapolate a trend line to a future conclusion, then the projection of that line is only valid if the progression of the contributing data series remain unchanged.

If for instance we go through a period where net migration halves from the projected levels, then the remaining progression of the trend is altered irrevocably. The longer and more sharp the deviation from trend, the more significant is the change in future outcome.

Now you really have to think this one through Keith. Carefully.