Proofhouse.com has Colt serial numbers you can look up.
That Colt cobra was made in 1976.
1965
1965
Colt data at Proofhouse.com
1967
Proofhouse.com has Colt sn data.
That sn doesn't fall in the Cobra range.
SN doesn't appear in sn tables
Made in 1951, second year of production.
You will have to call Colt
The date of manufacture is determined by the Colt model type and serial number. See: www.proofhouse.com/colt/index.html
Contact Colt Customer Service for a date of manufacture- no published data.