The Town shall document the number of lots containing legal two-family dwellings and multifamily dwellings in the R-40A District as of the effective date of this chapter by a count of documents issued by the Town through the effective date of this chapter establishing such dwellings. These documents shall include certificates of occupancy, prior to zoning letters, and Board of Appeals interpretations. Within seven days of the effective date of this chapter, the Town shall alert, by certified mail, property owners in the R-40A District of these procedures; whether or not Town records show their property contains a legal two-family dwelling or a legal multifamily dwelling; and, if they claim to the contrary, of their responsibility to document the legality of their dwellings.