Above year references are for Calendar Year, not Model Year.
|1953, 1966, 1979||A|
|1954, 1967, 1980||Z|
|1955, 1968, 1981||X|
|1956, 1969, 1982||V|
The charts indicate the Libby-Owens-Ford (LOF) automobile glass date of manufacture codes for their glass. The LOF logo will list the code as month/year. Examples: "KT" is April of 1957; "GX" could be April of 1968 or 1981. LOF was the major supplier of glass to General Motors and it is unlikely glass from other manufacturers was used on the assembly line.
LOF glass will also carry the American Standard specification rating codes for type and clarity - "AS1" for windshields, "AS2" for side door/vent and coupe rear glass.