It is official policy that there will only be one patriarch in each stake, but this is sometimes not the case if a patriarch moves from one stake to another. Also, a new one is sometimes called if the existing one is in poor health. As for your first question, I am having a hard time figuring this one out, but it appears that by the late 1800s at least there were many patriarchs. By 1910, there were possibly too many, because there was competition which was commented on by church authorities. It was then that fees for blessings were dropped. Also, early on people often had multiple blessings given throughout their lives.