I've just had a good look at the army records of both boys. They both left under Article 1142 on the 13 Feb 1907. They are 2 separate forms filled out by the same officers on each form.
I've added another iron to the fire, by placing a request on the New Zealand Rootschat. This search request is more for the movements around the time of the work done on the Mangahao Dam.
ADDING: The heading is also Robert Stevens/Seale
While Dad was quite intelligent and well read, as well as the training via books to become a radiographer, he had done some jobs as "fireman" and learnt to use farm machinery quite competently. He was good with a rifle - When he was between farms he ran low on food and had to shoot a top knot pigeon for food. I'm guessing that required some steadiness and accuracy.
Betty