Good question. I, too, have been diagnosed with Bipolar, and I am told that it is a life-time condition, which will always need treatment.

On the other hand, I would think PTSD and even anxiety could be cured. Or am I wrong on that?

I suggest you go ahead and tell your current psychiatrist about your concerns. I think they are appropriate, albeit your fears are somewhat exaggerated, I personally believe. After all, mistakes in diagnosis are made. I see no reason why an incorrect one, if that's the case, needs to remain in your records.

And why even tell anyone about the old diagnosis, if it is no longer confirmed? If anyone digs up the record, then they could be told about the incorrect diagnosis.....

I'd be interested in knowing what your psychiatrist says about it.