Usually for question when theres year betwern 20×1 to 20×5, and the question states to explan current dividend policy, do we have to calculate all the years ? Or just 20×1 and 20×5 will do ?
If you are asked to discuss the dividend policy then you should discuss all of the years.
If you are really asking about the calculation of the past dividend growth rate, then you only need look at the first and the last (as I explain in my free lectures on this).
It really depends on exactly what the question is asking.