Generally,  Black Powder > Smokless SAA :
   The visible difference is screw vs spring loaded cylinder latch retainer . Also changed was the steel and heat treatment. 
  The transition is Generally accepted to start in 1896 at s/n 164,100 . As of 1900 at s/n 192,000 , all subsequent SAA are * Officially Factory Certified * for smokeless. 
  In-between,  Colt used up parts on hand in various combinations . Individual guns in that 4 yr period could have randomly received all " smokeless " components . The closer to 192,000 the more likely.