This subchapter shall not be construed to limit the validity of a health care power of attorney executed prior to the effective date of this subchapter. A mental health power of attorney executed in another state or jurisdiction and in conformity with the laws of that state or jurisdiction shall be considered valid in this Commonwealth, except to the extent that the mental health power of attorney executed in another state or jurisdiction would allow a mental health care agent to make a mental health care decision inconsistent with the laws of this Commonwealth.