The D prefix was used from 1968 into 1977, and even afterwards using digits in front of the D.
D1 – D90,000…………….....1968
D90,001 – D330,000……..1969 -70
D330,001 – D420,000……1971 – Early 72
D420,001 – D510,000……Late 1972 – Early 73
D510,001 – D659,901……Late 1973 – Early 1974
D659.902 – D75000……...Late 1974 – Early 1975
D750,001 – D870,000……Late 1975 – Early 1976
D870,001 – D999,999……Late 1976 – Early 1977
2D00001 - 2D80,000…….1977
2D80,001 – 3D99,999……1978
4D00001 – 6D10,000…….1979
6D10,0001 – 7D10,000.…1980
7D10,001 – 9D44,500…...1981
9D44,501 – 17D8,900….…1982
17D8,901 – 21D0883……..1983