Sometimes once a year isnt enough, depending on what happens to it during the season. Like bumping it or having it tip over.
After a few years of hunting, some rifles dont need constant checking, they settle in on their own. I have one rifle here that hasnt needed an adjustment for over 15 yrs. But it has alot of shoulder time, and it hasnt been bumped or hasnt hit the ground for any reason.
I also have a friend that bought a new rifle 12 yrs ago, and he's still on his first box of shells. He goes deer hunting every year, sometimes he checks it every other year.
Some people arent hard on their guns.