There is no defined combination of spices in any set ratio for either. Ajoy lists 6 different Garam Masala formulae he uses for different purposes. Fish, Chicken, meat, Vegetable and kebab are the 5 I remember. Similarly, there is a multitude of mixed spice powders that are all called curry powder. There are common similarities just as there are variable differences in both.
BIR Mixed Powder may or may not contain curry powder as an ingredient just as readily as it can be considered a curry powder in its own finished blended state. Trying to pin a concrete definition to either is futile.
Garam Masala can be added early in the cooking process, towards the end, as a garnish / condiment, as an aromatic or a combination of these. Curry powder as an ingredient is usually, but not always, cooked.
There are certain spices that are always or usually present in each just as there are spices never or rarely found in one or the other. For example, Turmeric would almost always, or at least usually, be in any curry powder but probably never, or at best rarely, in Garam Masala. Black pepper would often be found in either.
Ajoy's 6th variation on Garam Masala is for biryani.