Best I can say is sometime after 1978. In 1978 serial #'s started with 1001L.
What year is a trooper mark 3 serial 10192j.With the serial number that you have provided,your Colt Trooper mark III was made in the year 1975.
your colt trooper was produced in 1968.
Your colt trooper was made in 1966.
The information I have shows that your colt trooper was made in 1961,but it does not show the B prefix to a serial number.
made about 1965
Impossible to answer without the serial number.
about 1973
1977
made about 1966
1972
Trooper model or 357 model serial # 68694 was produced in 1968. made about 1969
You can find out at Proofhouse.com in the Colt tables.