I think that success rate may be from season before last, I heard they had a record year this winter. I had the any bison tag a couple years ago. The season is long but for cows there is a bunch killed opening day and then they hit the park until the snow piles up and they return to the refuge, very few are killed in the National Forest in the mean time. You will likely do well but plan on being there the last week of the season. When I was there the cow's didn't start hitting the dirt until December 30th. This winter I guess they moved in early and stayed making for the record year.