Okla. Stat. tit. 18, § 381.45

Any association or federal association may continue to recognize the authority of an attorney-in-fact authorized in writing to manage or to make withdrawals either in whole or in part from a deposit account, whether of a minor or adult, until it receives written notice or is on actual notice of the revocation of such authority. For the purposes of this section, written notice of the death or adjudication of incompetency of such deposit account holder shall constitute written notice of revocation of the authority of the attorney.