Don't quote me on this, because I am DEFINITELY not a professional...

But I don't think a therapist can provide an official diagnosis, because they are technically not doctors. They do not have their doctorate degrees. I think that both psychologists and psychiatrists can provide diagnoses. I had a psychologist give me a full evaluation and then diagnose me after. I have also had psychiatrists diagnose me after a shorter period of time, like you experienced.

Just because they can't give "official" diagnoses to you though, doesn't mean you shouldn't take notice of their opinion. I believe that since therapists generally spend more time with you than a psychiatrist, they tend to know you better. If your therapist and pdoc are in contact with each other, that would be the best case scenario. Then your T could share his/her opinion with the pdoc, and vice versa.