How concentrated this event's inventory is among the sellers behind it: how many are active, what share the largest one and the largest three hold, how many tickets those shares are shares of, the concentration index and the band it falls in, and how much of the inventory could be attributed to a seller at all. Null when the event has no reading yet, which is the common case. No seller is named, ranked or identified, and the stored row holds no seller id. Costs one unit.