Your car is a 250S probably a 67 model. According to: Mercedes-Benz Production Model Book 1946-1983 by Robert Nitske, there were 2844 units made in 1965, 31564 in 1966, 37866 in 1967, 2014 in 1968, and 389 units in 1969 for a total of 74,677 units. My addition makes yours at the end of 1967.
Other than those who counted, MB didn't have a direct mechanism for year model attached to their chassis number until the US system reqired it.
Bosch Master, ASE Master, L1
33 years MB technician