This is more of a judgment call. Your GP likely was fairly sure of diagnosis in April. It would also not take the psychiatrist that long to make the diagnosis, so likely the psychiatrist communicated the diagnosis by April. If you are uncomfortable with this, you have the right to request that the medical records be corrected. Since the GP entered the subtype of schizophrenia, you could ask that it be amended to be consistent with Psychiatric report. Also, if the April diagnosis was made without input from psychiatrist you could ask the GP to change it to a "working diagnosis" or "provisional diagnosis". I would talk to GP informally before submitting official request.