Section 16. The state secretary shall, in the distribution of laws and documents to members of the general court, effect such exchanges among members as they shall direct; and he may employ such additional clerical or other assistance as may be necessary for the purpose. Copies of the laws and documents apportioned to members of the general court which remain undisposed of for three months after the end of the year in which they were issued shall revert to the commonwealth and be subject to general distribution.