The rule is a fraction, not a count. Two thirds of whoever was assigned to the job have to agree. How many that is depends on how much of the network is available to put on it, so it might be two of three, or five of seven, or six of nine.
It has to work that way, because this network starts with two graphics cards on a desk. A rule that demanded nine machines would have been unenforceable on day one and would have quietly become a rule about something else. A fraction holds at any size and gets stronger as more capacity joins.
The number assigned is written into the entry alongside the number that agreed, so nobody has to take our word for how thin the verification was on any particular day. A receipt that only went to three machines says so.