There's no manufacturer information available, as far as I know, for the exact ratio of the spices used in the curry powders we use. But they all have in common that the biggest components are cumin, coriander and turmeric. The reason we use curry powder in our mix powders is really for the other spices in the packet. You could conceivably reproduce most of the curry powders by suitable combinations of cumin, coriander, turmeric and garam masala (which, of course, has many variations in itself).
Edit: the point I was trying to make is that because mix powders are generally a combination of curry powder, cumin, coriander, turmeric and, usually in smaller proportions garam masala and paprika, that the other minor spices in the curry powder are swamped which is why different mix powders tend to (unexpectedly) turn out similar end results.