In the event all assessable project costs for any closed public improvement project have been paid and no debt service payments for obligations sold to fund any assessable portion of project costs of such closed public improvement project remain outstanding, then Special Assessment Collections shall be held in a fund to be used to guarantee bonds issued under Iowa Code Section 384.68 to the extent that any such bonds are outstanding. In the event that no bonds issued under Iowa Code Section 384.68 are outstanding, all remaining Special Assessment Collections shall be credited to reimburse the fund from which project costs were paid by the City on account of any deficiencies under Section 384.63.