The numbers are arbitrary. The list is not up to date, but has been changed since the start. It is SI that tells you the raw strength of the ship, but not who may be present to repair or be a gunner in any battles at any given time. The SI has made a huge difference over time as owners have upgraded, ranging from pathetically weak to dang!
That list is I believe the original purchasers.
But there is a more up to date one that JBK does his best with the aid of the ship owners to keep up to date. New owners can post in the thread so their entry is updated Info: - The History of Spacecrafts II | PlanetCalypsoForum