Wash. Rev. Code § 26.09.290
Whenever either of the parties in an action for dissolution of marriage or domestic partnership is, under the law, entitled to a final judgment, but by mistake, negligence, or inadvertence the same has not been signed, filed, or entered, if no appeal has been taken from the interlocutory order or motion for a new trial made, the court, on the motion of either party thereto or upon its own motion, may cause a final judgment to be signed, dated, filed, and entered therein granting the dissolution as of the date when the same could have been given or made by the court if applied for. The court may cause such final judgment to be signed, dated, filed, and entered nunc pro tunc as aforesaid, even though a final judgment may have been previously entered where by mistake, negligence or inadvertence the same has not been signed, filed, or entered as soon as such final judgment, the parties to such action shall be deemed to have been restored to the status of single persons as of the date affixed to such judgment, and any marriage or any domestic partnership of either of such parties subsequent to six months after the granting of the interlocutory order as shown by the minutes of the court, and after the final judgment could have been entered under the law if applied for, shall be valid for all purposes as of the date affixed to such final judgment, upon the filing thereof.
RCW 26.09.290
Part headings not law-Severability-2008 c 6: See RCW 26.60.900 and 26.60.901.