Only one accessory dwelling legally existing prior to January 3, 1961, per lot may be rented or occupied by persons other than bona fide domestic employees, provided that the Village Attorney certifies that official Building Department records confirm, or the Board of Appeals after a public hearing finds, that said accessory dwelling was legally in existence prior to January 3, 1961, and the Village Attorney or the Board of Appeals authorizes the Building Inspector to issue a certificate of occupancy so as to permit the rental or occupancy by nonemployees of the accessory dwelling.