Here's the info I've found on-line:
1955: 1-299
1956: 300-1649
1957: 1650-5549
1958: 5550-7049
1959: 7050-9099
1960: 9100-13099
1961: 13100-18799
1962: 18800-24799
1963: 24800-30799
1964: 30800-41399
1965: 41400-50499
1966: 50500-60999
1967: 61000-73799
1968: 73800-89999
1969: 90000-99999 (After serial number 99999, Colt started with E1001)
The very early Pythons had a non-prefix serial number. These ran from introduction up until 1969.
Starting in '69 Colt began adding letter prefixes to most of their guns, including the Python.
The post-69 guns used the "E" in front of the numeric serial, and was changed to AFTER the numeric number in 1975.
To further confuse things, Colt moved the letters back in front of the numbers in 1978. The higher the prefix the newer the gun is.
For instance, the prefix used was "E" in '69, "V" in '78, "K" from '80 thru '83, and "T" in '83 up to '85, when published records end.