Just as a matter of interest does anyone know what date the last car had a mixture control other than a choke? I'm guessing 1930.
I do not know of any car that ever had a (manually-controlled) mixture control.
AFAIK, manually-operated mixture control is limited to aircraft engines.
Early cars (prior to about 1932) had manual spark advance/retard controls, usually mounted on the steering column - so perhaps you are confusing the spark advance/retard mechanisms with mixture control.