I noticed many pre-1963 Chrysler 300 cars on the site do not have their letters in the titles. I thought this should be an easy fix as long as the right info is presented.

From Wikepedia (please verify)
1955 C (C represented "coupe" not all 300s were "C")
1956 B
1957 C
1958 D
1959 E
1960 F
1961 G
1962 H

Was that latter included in model name, or rather a kind of additional code?

My favourite was the '57 C:


The cars were named mostly alphabeticly. I ended with the 300 'L'.

Yes, but they continued beyond 1965 into 1971. I saw a 1970 being sold on the street recently. Red with white stripes. It looked nice.

I mean that just in the years prior to 1963, and excluding 1955, I think it should be easy to add the letter to the model name because there is no doubt that it is a letter series car. 1963 was the start of more mass-produced 300-series cars sans letter option.

I agree Leoz, Forward Look 300 C & D are beautiful cars!

Here is a nice 59 "E" example. Pay attention to the grille painted red on the inside:
http://www.richardandkarencarpenter.com/Auto-08 1959 Chrysler 300 E.htm

Okay, 1961 was the last year of the letter-only 300 series cars. Learn something everyday!