In Roy Jinks' "History of Smith & Wesson", page 179 he discusses the introduction of the Combat Masterpiece Models in .22, .32 and .38 caliber. He states that in the 1950 catalog, the new Combat Masterpiece was described as a "short action, target grade holster gun for law enforcement officers". I have always taken the "target grade" statement as meaning that the revolver had the micrometer adjustable sights, and I believe the trigger stop. That being said, two of my S&W's that have the most perfectly timed actions, and almost imperceptible end play and rotational play when locked are a Model 15-3 from 1977 and Model 27-2
from 1972. However both are from the Bangor Punta era where there was some inconsistency in the quality of the guns. I also had a Model 19-4 from 1978 that hardly had any rounds through it but was timed poorly and a bit loose so I sent it back to S&W a couple years ago for one of their tune ups and it came back perfect, tight, and with the barrel set back for a tighter B/C gap as well. My opinion is that the Model 15's from about 1972 on are like many other models, luck of the draw regarding how well they are put together. No better or worse than a Model 10 from the same period. From post WWII to about 1970 or so, it would be uncommon for any S&W K or N frame not to be assembled, and polished & blued damn near perfectly.