Cal. Probate Code § 4665

Except as otherwise provided by statute: (a) On and after July 1, 2000, this division applies to all advance health care directives, including, but not limited to, durable powers of attorney for health care and declarations under the Natural Death Act (former Chapter 3.9 (commencing with Section 7185) of Part 1 of Division 7 of the Health and Safety Code), regardless of whether they were given or executed before, on, or after July 1, 2000. (b) This division applies to all proceedings concerning advance health care directives commenced on or after July 1, 2000. (c) This division applies to all proceedings concerning written advance health care directives commenced before July 1, 2000, unless the court determines that application of a particular provision of this division would substantially interfere with the effective conduct of the proceedings or the rights of the parties and other interested persons, in which case the particular provision of this division does not apply and prior law applies. (d) Nothing in this division affects the validity of an advance health care directive executed before July 1, 2000, that was valid under prior law. (e) Nothing in this division affects the validity of a durable power of attorney for health care executed on a printed form that was valid under prior law, regardless of whether execution occurred before, on, or after July 1, 2000.