Read an interesting statistic for ADHD and depression. If you're diagnosed with depression first, there's only a 7% chance you'll be diagnosed with ADHD. But if you're diagnosed with ADHD, there's a something like a 44% chance you'll get diagnosed with depression.
I imagine there's a similar problem with any diagnosis that has overlapping symptoms--once you get an official diagnosis, all your symptoms are viewed as evidence of the diagnosis you got and not the diagnosis you didn't.
Me myself, I've gotten depression, bipolar, borderline, anxiety, but never autism and the occassional times I've gotten attention, it was never considered central to my issues (it is).
It would be one thing if they acknowledged how subjective diagnoses are, but they love to masquerade as a hard science that has definitively proven something. The field is a disgusting and cruel joke.