In that case I let my kids choose. (Actually, they mostly choose where to put things anyway….) – I know (although I can’t remember who the person is) that there is someone that is near the end of one century in my son’s book, and near the beginning of the next in my daughter’s book.
I have seen timeline books that use a grid, and a line for each person/event to show the entire span of that person’s life or the span of the event…. which I think would also be neat. (I think you end up a bit limited on how many events/people you can include though!)