b. A preliminary assessment may be entered within six years from the due date of the return or six years from the date the return is filed with the department, whichever is later, if the taxpayer omits from the taxable base an amount properly includable therein which is in excess of 25 percent of the amount of the taxable base stated in the return.
For purposes of this paragraph:
1. The term taxable base means the gross income, gross proceeds from sales, gross receipts, net worth, or other amounts on which the tax paid with the return is computed; and
2. In determining the amount omitted from the taxable base, there shall not be taken into account any amount which is omitted from the taxable base stated in the return if the amount is disclosed in the return, or in a statement attached to the return, in a manner adequate to apprise the department of the nature and amount of the item.