Per proofhouse.com with that serial number, it was made in 1928.
your colt detective special dates to the year 1949 by the serial number provided.
You will have to call Colt
That Colt ds was made in 1975.
You will have to call Colt to find out.
In 1965
1995
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.
Proofhouse.com has Colt sn data.
In 1931
Produced in 1973.
1968
1975