(1) A unitrust policy must provide the period used under RCW 11.104B.150 and 11.104B.160. Except as otherwise provided in RCW 11.104B.180(2)(c), the period may be:

(a) A calendar year;

(b) A 12-month period other than a calendar year;

(c) A calendar quarter;

(d) A three-month period other than a calendar quarter; or

(e) Another period.

(2) Except as otherwise provided in RCW 11.104B.180(2), a unitrust policy may provide standards for:

(a) Using fewer preceding periods under RCW 11.104B.150 (1)(b)(ii) or (2)(c) or (d) if:

(i) The trust was not in existence in a preceding period; or

(ii) Market indices or other published data are not available for a preceding period;

(b) Using fewer preceding periods under RCW 11.104B.160(2) (e)(i) or (ii), (f)(ii), or (g)(ii) if:

(i) The trust was not in existence in a preceding period; or

(ii) Fair market values are not available for a preceding period; and

(c) Prorating the unitrust amount on a daily basis for a part of a period in which the trust or the administration of the trust as a unitrust or the interest of any beneficiary commences or terminates.