Always mucking things up. I have only ever been on the law enforcement side of RCW 9.73 (assisting in obtaining one party consent authorizations in a bona fide investigations) so I cannot claim to have all the answers. However, I always try to think through all of the consequences, intended and not.
I can imagine a scenario where someone objects to being recorded but their later actions show that they have waived the objection. Even so, I would never advise one of you to continue to record after an objection has been expressed. The reason is that violation of RCW 9.73 1) is a crime, albeit a gross misdemeanor, 2) could result in civil liability and, 3) any recording you obtain in violation of RCW 9.73 will probably not be admissible in any legal proceeding.
There is a bunch of case law in this area (Westlaw returns 197 cases on a search for "RCW 9.73") but a quick scan doesn't reveal anything on point (legalese for a case that matches your argument). What is consistently expressed is that it is unlawful to record a private conversation without the consent of all parties. State v. Townsend, 147 Wn.2d 666, states "This statute is considered one of the most restrictive in the nation." Given that, do you want to make yourself a test case?
The result in any case is going to depend on the facts and we all know how many times the facts can get sideways. And since this lawyer sees this issue one way I can guarantee you that there is another lawyer (or six) out there who will see it in just the opposite way. That's what makes the law so much fun.
RCW 9.73.030
1) Except as otherwise provided in this chapter, it shall be unlawful for any individual, partnership, corporation, association, or the state of Washington, its agencies, and political subdivisions to intercept, or record any:
(a) Private communication [SNIP] without first obtaining the consent of all the participants in the communication;
(b) Private conversation [SNIP] without first obtaining the consent of all the persons engaged in the conversation.
RCW 9.73.050
Any information obtained in violation of RCW 9.73.030 or pursuant to any order issued under the provisions of RCW 9.73.040 shall be inadmissible in any civil or criminal case in all courts of general or limited jurisdiction in this state, except with the permission of the person whose rights have been violated in an action brought for damages under the provisions of RCW 9.73.030 through 9.73.080, or in a criminal action in which the defendant is charged with a crime, the commission of which would jeopardize national security.
RCW 9.73.060
Any person who, directly or by means of a detective agency or any other agent, violates the provisions of this chapter shall be subject to legal action for damages, to be brought by any other person claiming that a violation of this statute has injured his business, his person, or his reputation. A person so injured shall be entitled to actual damages, including mental pain and suffering endured by him on account of violation of the provisions of this chapter, or liquidated damages computed at the rate of one hundred dollars a day for each day of violation, not to exceed one thousand dollars, and a reasonable attorney's fee and other costs of litigation.
RCW 9.73.080
(1) Except as otherwise provided in this chapter, any person who violates RCW 9.73.030 is guilty of a gross misdemeanor.