Wash. Rev. Code § 35.23.545
Proceedings attacking the validity of the consolidation of a city of the second class or the annexation of territory to a city of the second class shall be by quo warranto only, instituted by the prosecuting attorney of the county in which the city is located or by a person interested in the proceedings whose interest must clearly be shown. The quo warranto proceedings must be commenced within one year after the consolidation or annexation proceedings complained of and no error, irregularity, or defect of any kind shall be the basis for invalidating a consolidation or annexation after one year.
RCW 35.23.545
Validating-1923 c 153: "All proceedings for the consolidation of cities of the third class and for the annexation of any unincorporated territory described in any abstract filed with the secretary of state in any such annexation proceeding to a city of the third class heretofore had, or attempted to be had, and over which such consolidated cities or annexed territory such city has exercised jurisdiction for a period of one year after the filing of such abstract with the secretary of state, are hereby ratified and validated as of the date of filing such abstract, irrespective of the fact that such consolidated cities, or any part thereof, are separated by a body of navigable water or that such annexed territory, or any part thereof, is separated from such city by a body of navigable water, and irrespective of any failure to file a petition for such consolidation or annexation, or to give proper notice of election or of any other defect occurring in such consolidation or annexation proceedings, and all territory so sought to be annexed is hereby declared to be a part of such annexing city as of the date of filing such abstract, and such cities so consolidated are hereby declared to be one municipal corporation as of the date of filing such abstract. All proceedings since the date of the filing of such abstract heretofore had or attempted to be had by any such city within or including such annexed territory, or any part thereof, in the creation of local improvement districts and the making of local improvements, the levying of special assessments and the issuance of bonds therein and also in the levy of taxes, making of contracts, incurring of indebtedness and the issuance of bonds therefor are hereby ratified, validated and confirmed. PROVIDED, That nothing in this act contained shall affect the rights of any parties in any proceedings now pending in any court of record in this state and the rights of such parties therein shall be determined and adjudicated as the same existed prior to the passage of this act." [ 1923 c 153 s 2.] This applies to RCW 35.23.545.