With respect to mortgages, I think the answer lies in a change in the Title Examination Standards in 1994. Before September 1, 1994, the corporate seal was required. After that date, the revisions eliminated that requirement.
Title Examination Standards
Chapter 1, App.
Chapter 12. Corporations
§12.2. Rebuttable Presumptions Concerning Corporate Instruments Executed in Proper Form.
If a recorded instrument from a corporation is executed and acknowledged in proper form, the title examiner may presume that:
A. the persons executing the instrument were the officers they purported to be,
B. the officers were authorized to execute the instrument on behalf of the corporation,
C. the corporation was authorized to acquire and sell the property affected by the recorded instrument, and
D. the corporation was legally in existence when the instrument was executed.
From and after September 1, 1994, recorded instruments must be signed on behalf of a domestic corporation by a president, vice president, chairman or vice chairman of the board of directors. A corporate instrument executed in another state may be accepted if it is executed either by the proper officers under Oklahoma law or by the proper officers under the laws of the state where the instrument was executed.
Before September 1, 1994, corporate instruments were required to be executed by a corporate president or vice president, attested by a corporate secretary or assistant secretary, and impressed with the corporate seal. Instruments from banks could be attested by a cashier or assistant cashier.
Authority: 16 O.S. §§ 53; 93.
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This Standard can be found
here.