Iowa Code § 434.14: Amended statement.

The department of revenue may demand, in writing, detailed, explanatory, and amended statements of any of the items mentioned in section 434.2, or any other items deemed by the department important, to be furnished the department by such railway corporation within thirty days from such demand, in such form as the department may designate, which shall be verified as required for the original statement. The returns, both original and amended, shall show such other facts as the department, in writing, shall require.