(b) The amount of license taxes imposed by this chapter shall be assessed or levied, or the overpayment, if any, shall be credited within three years after filing of the monthly statement, or within three years of the due date prescribed for the filing of the statement, whichever is later. No proceeding in court without assessment for the collection of the taxes or the enforcement of the liability shall begin after the expiration of the three-year period. Where the assessment of the tax imposed by this chapter has been made within the period of limitation applicable thereto, the tax may be collected by levy or by a proceeding in court under chapter 231; provided that the levy is made or the proceeding was begun within fifteen years after the assessment of the tax. For any tax that has been assessed prior to July 1, 2009, the levy or proceeding shall be barred after June 30, 2024. Notwithstanding any other provision to the contrary in this section, the limitation on collection after assessment in this section shall be suspended for the period:
(1) The taxpayer agrees to suspend the period;(2) The assets of the taxpayer are in control or custody of a court in any proceeding before any court of the United States or any state, and for six months thereafter;(3) An offer in compromise under section 231-3(10) is pending; and(4) During which the taxpayer is outside the State if the period of absence is for a continuous period of at least six months; provided that if at the time of the taxpayer's return to the State the period of limitations on collection after assessment would expire before the expiration of six months from the date of the taxpayer's return, the period shall not expire before the expiration of the six months. As to all tax payments for which a refund or credit is not authorized by this section (including, without prejudice to the generality of the foregoing, cases of unconstitutionality), the remedies provided by appeal or by section 40-35 are exclusive.