Persons hospitalized prior to September 15, 1964.

Subject to subsection (b) of this section, the provisions of sections 21-546 to 21-551, subchapter V of this chapter and sections 21-585 and 21-588 apply to a person, who, on or after January 1, 1966, is a patient in a hospital in the District of Columbia by reason of having been declared insane or of unsound mind pursuant to a court order entered in a noncriminal proceeding prior to September 15, 1964. A request made by a patient referred to in subsection (a) of this section for an examination authorized by section 21-546 may be made on April 15, 1966, by the patient, or his attorney, legal guardian, spouse, parent, or other nearest adult relative, and not more frequently than every six months thereafter.