You have the opposite of a parts gun. You have what is essentially a factory custom. At this point we don't know what the exact original configuration was, but the major clue is in the letter where it was called a Special Production Revolver.
It is a combination of a 25-5 frame (later 25-5s were made without barrel pins and have the three letter /four number serial "numbers"), a 25-9 cylinder, and a leftover barrel from the Georgia Highway Patrol commemorative revolvers of 1987 (Model 26-1s).
There were 800 of the Georgia Commemorative revolvers made. They were all decorated. There were 40 more revolvers that are plain that were over runs. There were also a very, very few leftover barrels. This revolver was completed with one of them.
If I were to guess I would believe it was made in that configuration in 1999 either as a favor to that salesman or as a possible prototype for another run of revolvers in the configuration of the Georgia guns. The return to the factory in 2004 was to clear it off the salesman's account. It being shipped to a company in Georgia is also an interesting clue. The lanyard loop is also a clue.
You have a unicorn.