Whenever any taxable real estate shall be omitted to be assessed at the triennial assessment, the elected or appointed assessor, on notice thereof, shall forthwith assess and return the same to the proper office, which assessment shall be subject to appeal, and shall continue until the next triennial assessment, and its proper proportion of all taxes to which such real estate is liable, levied after such assessment, shall be laid thereon.
72 P.S. § 5020-406