I would say from my own experience that this is ODD and I have never seen one before, but that certainly doesn't mean it isn't all totally legitimate, especially when we consider that it's S&W and also that this was shipped outside of North America.
What I find include all of these:
--AVP serial prefix range for a 17-6 is odd, in my experience and I would much more readily believe it were a 17-5
--the standard ribbed target barrel was the norm for the first half (somewhat less than half) of the dash-6 variant, however I have never, NOT EVER seen the Combat stocks and the standard ribbed target barrel together. The full lug barrel and the combat stocks came at exactly the same time, at least in all mt travels and I've been following these since I got mine in 1988.
--the four inch barrel on a 17-6 is certainly less common, but so is the ramped front sight. The ramped front sight was usually a characteristic of the Model 18 but at this time, the 18 was not in production.
--the SCSW4 suggests that the full lug barrel/combat stocks did not arrive until 1990, and the AVP-serial prefix would tend to predate 1990 by at least a small handful of years. Of course, S&W and especially the three-alpha SN prefix always leaves as many questions as answers.
In looking over the whole thing, the only answer that seems to make quick and easy sense of things (to me!) is that this revolver is actually a 17-5 and someone added the combat stocks.
In the end, the most accurate answer is almost certainly that we have all long ago agreed to "never say never with S&W!"
