Well, if the 2" barrel became available in the late 1890's, and your firearm shipped in 1884, then it cannot be original to the gun. I believe Smith & Wesson becan stamping rework dates on the frame during the first decade of the 20th Century. I want to say the earliest guns with such dates that have been identified have the two digit year of 09, meaning 1909, but it might have been a few years earlier than that. Which means that your barrel was installed before restamping of dates became commonplace or, if later, the frame escaped restamping.
Can you provide good photographs of the barrel serial number so we can determine if the numbers appear to be factory in origin?
You might want to contact the SWHF to see if they have information on when this might have been done. I have a revolver with the star on it but no date, for some unknown reason, and they still provided me with a multitude of information on the work done on the firearm, this being in the autumn of 1929.
However, without any documentation to prove any of this, it makes it difficult to assign a value to this, other than to someone who might find it to be "neat" and pays a price that reflects outside later modifications.