I should note that I have units from Classic, Revised Edition, 1941, & 1940 with some significant color variations. So in some cases I may be matching a different edition. So for example, I think the early UK units are darker than my 1940 versions explaining why I choose a darker color. Plus with the cheap paint, I worry that the color consistency is less consistent bottle to bottle.
When I indicate A + B paint colors, I mix then 1 to 1.