In addition to S&W shipping them that way from the factory, you could also buy a trigger kit to install one yourself in your DA K38. As far as I know, only a factory letter will tell you for sure which way one came, unless it's a dash variation way after S&W quit shipping complete K38 SA's on a regular basis, then it's mostly like from the factory kit..

I have several K38 Masterpieces; it's the gun that got me into pistol shooting in the early 70's, and still my favorite. Not too heavy or too light, it's a plinker's delight.

My one example of a SA K38 is easier to cock; I would think that would be appreciated over the course of a match. It's my most accurate one, but with my skills that's not saying much

Really one of the most fun shooters of the classics, or any other generation.