Okla. Admin. Code § 710:10-16-4
In order to be eligible for the exemption the individual must apply in the initial year the exemption is requested at the county assessor's office by completing Form 998-C, Application for Unremarried Surviving Spouse of Veterans Deceased in the Line of Duty Property Tax Exemption.The application should be made between January 1 and March 15 in the same manner as the homestead exemption. However, if a county assessor becomes aware of an otherwise qualified applicant at any time during the current tax year or the exemption is transferred to another homestead eligible property the county assessor shall, upon compliance with all identification and qualification criteria, make the appropriate adjustment. Providing all homestead and other requirements are met, if an otherwise qualified applicant is in receipt of the Form DD-1300 certifying they are the surviving spouse of military personnel who died in the line of duty, on or before the date of the application, the homestead property is exempt for the remainder of the current year. If an otherwise qualified applicant is discovered after the tax roll has been certified, a tax roll correction shall be made pursuant to 68 O.S. § 2871(C)(2). Any application denied by the county assessor shall be subject to the same protest procedure as provided for homestead exemption. If the qualified unremarried surviving spouse subsequently remarries, they shall immediately notify the county assessor of the change in marital status. Failure to notify the county assessor may result in the loss of future homestead exemptions pursuant to 68 O.S. §§ 2892(K) and 2900. The application must be filed in the year requested, filing for previous years is prohibited pursuant Oklahoma Constitution Article 10 § 22A.
Okla. Admin. Code § 710:10-16-4