H confirmed 1921 to 1971

I confirmed 1921 to 1938

J confirmed 1930 to 1960

K confirmed 1924 to 1927

L confirmed 1934 to 1958

M confirmed 1931

N confirmed 1927 to 1956

O confirmed 1926

P unconfirmed before 1953

    > P code from 1953 to 1965 used with variable weight, assumed only for Commercial

Q confirmed 1926

R single letter R confirmed as Replacement 1924 to 1926

   single letter R assumed to be Replacement 1934 to 1936

   used with weight/class code; confirmed 1936 to 1958

      i.e., "RD" is replacement class D, passenger

             "RX" is replacement Dealer.

S confirmed 1930 to 1935

T confirmed 1927

U&V Earlier years: Government-owned Truck or Trailer;

        Later years: School Bus. School Bus believed to have started in 1948.

            Research ongoing to determine which years each designation was used.

W unknown early years; possibly same as U & V

 W Disabled (wheelchair) confirmed 1969 to 1977

X used 1921-current, except 1961 to 1965

Y confirmed 1964 to 1970

Z confirmed 1925-current; all-numeric exist in 1940's - assumed overflow after Z999