Colt made target versions of their 1892 New Army/Navy revolver before Smith & Wesson introduced they're Model 1896 .32 during that year, but it is unquestionably the first S&W hand ejector target variant. Apparently the rear sight was made before they standardized the design, or they used an older prototype they still had on hand even newer ones were available. Last but not least it may represent an improved design that never went into production. The revolver itself is not common, as it was only made between 1896 and 1903, with total production around 19,712. Of those very few were target models, and among those that still exist, this one may be unique - or near so.
The lesson to be learned is if you come across something that is unusual as was this example, get it lettered. The one thing I'm sure of is the increase in the revolver's value far exceeds the cost of the letter.