Dating road maps combination of sedating and non sedating antihistamines
CONOCO used Gousha maps continuously from 1927 to 1981, so by looking at the Conoco-CO-Spreadsheet page you can see the complete Gousha map code sequence for CONOCO Colorado maps.
I don't know the meaning of these letters, but they can sometimes confuse dating maps by map code.
Maps from the 1930s will often have three-digit codes containing just the month and last two digits of the year, generally in that order; 336 = March 1936, for example. 15 1957 (date  last two digits of year reversed [75 = 1957] month ) 124511 = Nov. Clason maps are notorious for having no date information.
12, 1954 (date  last two digits of year reversed [45 = 1954] month )1744 = 1947 ["74" reversed is "1947"] 218412 = 1948 20353 = 1953 1354 = 1953 C-11558 = 1955 15658 = 1956 C-15857 = 1958 C-1859 = 1958 C-5361 = 1963 After this date they seem to use more standard dating, e.g., 9-67 = 1967. Instead, various elements of the maps changed over time.
Geographers' also used an alphabet code: As with Geographia, the code then takes a MM. GE is October 1946), usually placed in the bottom left of the map itself.
The major change on the maps is the extent of railways portrayed, which varies enormously as the maps move from the 1830s to 1880s (? The date printed on the map refers to the underlying map and not to that of the railways, which were generally added in manuscript in red at some stage between the map printing and the sale of the copy; the dates on the maps and the extent of railways do not have a linear correlation, as some maps with earlier dates have more railways than maps with later dates.
Arrow Map Incorporated Automobile Club of Southern California Buddhist Calendar Dates California State Automobile Association Clason Road Maps Diversified Maps General Drafting Company George F.