Also, are we REALLY going to split hairs over it? TOS is full of contradictory statements. It's ironic how people get hung up on the 12 or 13, and feel strongly about it one way or the other, yet completely ignore the statement Kirk makes in "Our authority is the United Earth Space Probe Agency." This is never mentioned before, or since, and it is commonly accepted the real authority that should have been mentioned is either the UFP or Starfleet Command. That is why I don't think the fleet is necessarily limited to 12 Constitution class ships (and it is likely more when you count other classes), neither by Kirk's statement, nor do I exclude the possibility that the fleet of Constitution class ships increases or decreases depending on the time you are talking about in TOS (new builds coming online, others getting destroyed, etc).