If you are referring to the Varmint Hunters magazine club, you must have your shot witnessed by another member. Other than that it is based on a honor system.
When I was first getting into the longrange game I shot a crow @ 495yds (lasered & witnessed) with my 6mmAI heavy varmint rig. My buddy was so excited because he figured that I would be the first guy that he knew that would make the 500 yd club. I hated to disappoint him but although I was rather proud of the kill it still wasn't 500 yds and I wasn't about to claim it was. You know - like taking pride in a beautiful 10 pointer even though you killed it with the bumper of you 86' Chevy. Suggesting that it was your bow kill really doesn't do much for your ego.
I and two friends all did it in one day on a prairie dog town. One friend did it right away with a 22-250, the other used a 308 w/110 vmax and I was last useing the friends 308 as I couldn't connect w/mine/ran out of ammo. It really helps to get a no wind day. I plan to do it again with a 223 when I get a no wind day.