Sts. & Hy. Code, § 9164

If in order that the principal amount of outstanding bonds not canceled in the refunding proceedings which is payable annually and interest thereon shall equal the principal amount of assessments made under the original proceedings which are payable annually and interest thereon, it is necessary to reduce the amount of any bond or interest coupon, an appropriate notation showing the amount of reduction shall be written, printed, or stamped upon the face of each bond or coupon reduced in amount. The remaining amount of such bond or coupon shall be payable, collectible, and enforceable in accordance with the provisions of the Improvement Bond Act of 1915.