Are you sure the serial number is correct? The Colt detective special was first produced in 1927 with a starting serial number of 331000,The Colt police positive special from which the Colt detective special was derived from with the serial number 153817 was made in 1918
The Colt detective special was derived from the Colt positive special in 1927and the starting serial number for that year was 331000 so the serial number you show of 3021 does not match up as a Colt detective special. Now if the serial number was 383021 then it was made in 1930.
The serial number you give is too low to be a Colt detective special. Colt detective specials were produced in 1927 starting with serial number 331000.They were cut-down versions of the Colt police positive specials. Now the Colt police positive special with that serial number was made in 1912.