The amendments to the durable power of attorney law of Missouri enacted in 1997 are effective August 28, 1997, and shall apply, except that, as to powers of attorney executed prior to January 1, 1999, the laws in effect prior to August 28, 1997, shall apply if such prior laws shall be more favorable to construing said powers of attorney to:
(1) Be durable; or
(2) Grant a power sought to be exercised by the attorney-in-fact.