The way my dr explained it to me was, we're all on a spectrum, our diagnoses are just a way to explain our collections of symptoms; that was her philosophy anyway. She thought labeling me w/ bipolar disorder was too specific for my collection of symptoms. I'd guess if your mood issues are your primary problem and they happen to be accompanied by anxiety, your going to get stuck w/ mood disorder NOS but if you have general anxiety and your depression or mood swings are more a result of living w/ anxiety they'll stick you w/ a GAD diagnosis, since the depression is secondary, like you said. Most of my issues were anxiety driven but I definitely have bipolar stuff going on. My dr felt like my hypomania was showing up as anxiety and anger but mostly anxiety (wish i'd gotten the euphoric mania but that was never my problem lol). With mania a mood disorder diagnosis is pretty much a given. I've really never been diagnosed w/ GAD, that I know of. And no I dont mind you asking at all, I had body dysmorphic disorder w/ exercise bulimia which is an anxiety driven disorder (dont know if its technically an anxiety disorder). And I was diagnoised w/ PTSD. But I've had anxiety ever since I was in grade school.
EDIT: hey I just read your post in the other folder and I just wanted to say, DONT WORRY about this diagnosis, if you were diagnosed w/ a mood disorder, it really doesnt have to be a big deal, doesnt have to mean you're bipolar, there are some pretty mild forms like cyclothemia, and personally I'd rather get one diagnosis of mood disorder NOS than tell someone i've got bipolar, ptsd, an eating disorder, etc, etc, etc, etc! lol That sounds a lot worse doesnt it? Your symptoms are the same as they were before the diagnosis, being labeled w/ mood disorder doesnt make you any Crazier.
So try not to let it freak you out.