I guess I blame the Blue Book for this "First Model" and "First Issue" business. What are supposed to be the characteristics of each "model" or "issue?" The Blue Book ignores those issues.
One could say the DS introduced in 1927 with a square butt was the "First Model". Would the round butt introduced in 1933 be a "Second Model?" Would the Post-War revolvers with the ramp front sight (replacing the Pre-War half-moon front sight) be a "Third Model?" Would the change in 1966 to the short frame be a "Fourth Model?" Would the shrouded barrel introduced in 1972 be a "Fifth Model?"
Although I think the category too large with too many significant variations, many consideer that the 1927 through 1965 are the "First Model" because the frames are the same length. The short frame 1966 through 1972 unshrouded guns are the "Second Model," while the shrouded barrel guns are the "Third Model."