If they ever re-assess, could they seek money for prior years for their mistake or only going forward?
I did a bit of research on this question.
RCW 84.40.040 says that the assessor must finish "placing valuations on all properties" by May 31st for most properties and by August 31st for some other properties.
RCW 84.40.320 says that the assessor must provide a listing of assessments to the county board of equalization by July 15th, except that for the properties where the assessor had until August 31st to assess them, they don't need to be provided to the board of equalization until August 31st pursuant to RCW 36.21.080 and RCW 36.21.080.
These provisions appear to place a deadline on when the assessor is free to change the assessment. However, the case law says that these provisions are not mandatory and that the true deadline is that the assessment must be made "in the year before the taxes are to be levied, including an allowance for time in which to appeal":
Niichel v. Lancaster, 97 Wn2d 62 (Wash Sup Ct 1982). This still appears to prevent retroactive changes though.
RCW 84.48.200 says that the department may make rules for the administration of the county boards of equalization.
One such rule is WAC 458-14-116. It says that the board may adjust upward the valuation of a property, either in response to a petition being filed, WAC 458-14-056, or on the board's own initiative. WAC 458-14-056 only appears to contemplate the taxpayer being able to file a petition, not the assessor, but the assessor could invite the board to exercise its power to act on its own motion. However, in either case, WAC 458-14-116 says that such upward change "shall become effective thirty days after the date of service or mailing of the notice of the adjustment". This appears to rule out retroactive increases by the board of equalization.
RCW 84.48.065(1) contains another statutory authority for modifying assessments. This statute provides that "The county assessor or treasurer may cancel or correct assessments on the assessment or tax rolls which are erroneous due to manifest errors in description, double assessments, clerical errors in extending the rolls, and such manifest errors in the listing of the property which do not involve a revaluation of property...".
This is not the most clear statute. It's somewhat unclear whether the condition that the errors "do not involve a revaluation of property" applies to all of the grounds for change, or only the last one.
In an "unpublished" opinion with purportedly no precedential value, the Court of Appeals for Division One appears to suggest that the condition applies to all grounds but that the prohibition on "revaluation of property" only prevents the assessor from making new subjective judgments and does not prevent the correction of certain factual errors that, when corrected, increase the amount of the assessment:
Legacy Partners Riverpark Apts Buildings A/b, Llc, App v. King County, Res, 69073-6 (Wash Ct App 2013). The Court did not articulate a very clear test to determine whether a given correction is permissible.
Many courts in the US have local rules that purport to allow the court to issue decisions without precedential value. The constitutionality of these rules has been questioned on various grounds.
Anastasoff v. US, 223 F3d 898 (8th Cir 2000) holds that these rules are unconstitutional in the federal court system, but that decision was subsequently vacated for mootness, 235 F3d 1054, which latter opinion says that the question of the status of "unpublished" opinions remains open. No case that I know of has discussed the constitutionality of these rules in state courts.
The
Legacy Partners case is actually a good example of why "unpublished" opinions can be a bad idea (which is, of course, separate from whether they are legal). In
Legacy Partners, the Court was apparently confronted with a novel issue with no cases directly on point. The Court must have recognised that its decision, if precedential, would have effects in many other situations. But apparently the Court wasn't prepared to take on that responsibility, so it simply asserted that its decision would not be precedential. If you were a party to the case, wouldn't you question whether the Court really did a thorough job contemplating the issues, if it didn't think its decision would ever be cited again? The ability to issue an unpublished opinion arguably gives the Court the power to absolve itself of its judicial duties when it feels they would be too difficult to exercise, which may be inconsistent with the proper role of the courts in our legal system.