There’s no official answer that I know of.  A&A is such an abstracted game that, in one sense, it would be meaningless to say that game unit X corresponds to real-world military (or naval) formation Y.  Given the scope of A&A Global 1940, however, the various unit types on the map would roughly correspond to large formations if we were to assume that the allocation of units in the rules corresponds to real WWII numbers.  As an example, Germany’s invasion of the USSR was carried out with over 150 divisions – so from that perspective, the small number of sculpts on the actual board could at best only correspond to army groups.  At that level, it shouldn’t even be possible to differentiate between the components of the army groups, nor even of their consitutent armies or corps; the highest-level tank formations in WWII were, I think, armoured divisions and (one level further down) tank brigades.  So one way to look at the game would be to imagine that we’re not actually seeing the military formations themselves, but rather a patchwork picture showing some of the elements of those formations, with some of these elements being high-level ones and others being lower-level ones (like tank brigades).