T478xx was made after 1985.
This is as far as publicly available records go.
The last number shown in 1985 was T34453.
To get an actual date, call Colt during normal business hours.
They will give you a date of manufacture, but NO other info.
1-800-962-COLT
On value, that depends entirely on actual condition, based on the percentage of original finish, and any scratches or wear.
As a rule of thumb, a Python usually runs from "about" $600 to $1200.