why is much of the history of the lottery and the black box uncertain and vague? why does Mr. summers have to ask a question that he and everybody else already know the answer to ?

One of the bigger themes of this story is tradition and the irony this town has for it. All the trappings of the lottery (singing, chanting, nice box, paper in the box) have fallen by the wayside. Interestingly the only thing people really care about is the stoning itself. Mr.Summers asks people questions, he knows the answer to, as a matter of "official" protocol. In reality, he only asks questions that will embarrass people, specifically women who do not have a "man" to draw for them.