Pesachim 97: Taking Refuge in a Cemetery

On Shmuel's discussion of a Korban Chatat, and the 5 cases when an animal that was designated for the korban can't be used, and it's put to death instead of living out its days grazing, until it gets a blemish anyway. Plus the policy of sending most out to graze, if disqualified. And the parallel application of these same cases to the Korban Pesach (they become korbanot shelamim), but still, most go to graze. With caveats on Shmuel's position. Plus, which factor wins out when there's a replacement korban?