If the assessor requires an assessee to describe personal property in such detail as shows the cost thereof but the assessee omits to report the cost of the property accurately, notwithstanding that this information is available to the assessee, to the extent that this omission on the part of the assessee causes the assessor not to assess the property or to assess it at a lower valuation than he would enter upon the roll were the cost reported to him accurately, that portion of the property as to which the cost is unreported, in whole or in part, shall be assessed as required by law. If the omission is willful or fraudulent, the penalty and interest provided in Sections 504 and 506 shall be added to the additional assessment; otherwise only the interest provided in Section 506 shall be so added.