Nothing in this chapter may render more difficult the collection of outstanding bonds or notes of any drainage organization or impair the obligation of any contract made by the organization or defeat any vested property right of the organization. No assessment of supplemental benefits nor any reassessment of benefits may disturb any previous assessment for the cost of construction while bonds or notes based on the construction are unpaid. Assessments shall remain liens upon the same lands and claims against the same corporations in the same amounts as when first assessed and recorded, until the bonds and notes based on the construction are paid or refunded.