Again, your stated- Joseph Smith was not attempting to correct the NT to make it conform to the earliest possible manuscripts, but to make it conform to the original manuscripts through inspiration from God.
So smith made the KJV 'conform' to the 'origional manuscripts' Smith left the Comma in the KJV - did not delete it out as he did other portions of the bible. By default it means the passage was part of the origional ms.
I was not implying perfect conformance on the part of the JST, but rather an improvement over the KJV. If that was not understood, I make the clarification now.