[Mr70]

That's right.The deciding factor was what state/region the vehicle was going to be bought brand new in,i.e.(Calif.)
If that 1970 vehicle was assembled in LOS or NOR,and ordered by a waiting dealer in Calif.then it was assembled w/NA-9 @ the factory and would appear on it's buildsheet.
If the same vehicle was assembled in LOS or NOR,and ordered by a waiting dealer in Chicago,then it was not assembled w/NA-9 at all....but if that dealer in Chicago received it,and then did a dealer trade with a dealer in Calif.,then that Calif. dealer had to install NA-9 on it in it's service bay before it could sell it to it's buyer in Calif.
That's why many nickname NA-9,California Emissions.