From: east coast, usa
D21 is designed so that the player doesn't find it necessary to keep units in a corps or army organization. It isn't convenient, and it isn't historic, because most if not all units switched subordination thru out the war.
Now, maybe you are like me and you like to keep an organization. For me it is pretty much mandatory, I can't play with out it. But do you want me to color coordinate all the units for you, and then you have to stick by that setup the whole game? I wouldn't want your setup, so I guess you wouldn't want mine!
When I play D21 I keep the attached file open, and also a printed version in front of me. It's as they say - anal to do so, but I'm OOB OCD.