All citations must be disclosed on N-400. The question asks whether applicant was ever cited, arrested or detained. Ever means any time in lifetime, anywhere.
Not disclosing citation is a problem in itself (misresepresentation), even if citation is nothing major, like speeding.
Yes, @Fobosdaemios you should list all citations. You can bring an errata sheet for your N-400, which is a simple page with table consisting of columns:
Part #, Question #, Current Answer, Corrected Answer.
You should have done some effort and get records from county in Washington state. Depending on officer, they may be OK with your explanation, especially if it was 10 years ago. But some may ask for records / proof.