right, so, by that logic, if you have tumors but never test to see if they are cancerous or not you can't have cancer because you have never been diagnosed with it, and the tumors will be unable to kill you.
having a condition and KNOWING you have a condition are two different things. if you have cancer and don't get tested, yeah, you can't go around telling your friends you have cancer, but that isn't going to stop the cancer from killing you. same with depression. if you are depressed but don't get tested, then, yeah, you can't go around saying you are clinically depressed, but that doesn't mean you aren't going to suffer from the depression.