(a) The value of all motor vehicles returned for taxation during the previous calendar year shall be added to the regular digest at the time the regular digest is transmitted to the commissioner or at such other time as the digest is required to be compiled.

(b) The value of all mobile homes returned for taxation during each calendar year shall be added to the regular digest at the time the regular digest is transmitted to the commissioner or at such other time as the digest is required to be compiled.

(c) The total of the regular digest and the value of returns required to be added pursuant to this Code section shall constitute the tax digest.