The dash 2 never changed into a dash 3. S&W made so many Model 10s that they gave different dash numbers to light tapered standard barrel and heavy barrel Model 10s. Dash 2 had the standard barrel during the same time period that the dash 3 had a heavy barrel. Dash 2 changed into the dash 4 then dash 5. Dash 3 changed into the dash 6.
SCSW 3rd. ed. P.174
What year did the dash 2 change to the dash 4?