All bonds or other evidences of debt having a fixed term and rate of interest held by an insurer may, if amply secured and not in default as to principal or interest, be valued as follows:
(1) If purchased at par, at the par value.
(2) If purchased above or below par, on the basis of the purchase price adjusted so as to bring the value to par at maturity and so as to yield in the meantime the effective rate of interest at which the purchase was made, or in lieu of such method, according to such accepted method of valuation as is approved by the commissioner.
(3) Purchase price shall in no case be taken at a higher figure than the actual market value at the time of purchase, plus actual brokerage, transfer, postage, or express charges paid in the acquisition of such bonds or other evidences of debt.
(4) No method of valuation shall be inconsistent with any applicable valuation or method used by insurers in general, or any such method then currently formulated or approved by the National Association of Insurance Commissioners or its successor organization.