Im not from WA but i did spend six months and went all the way to the Director of the MD DNR to get my Rickter registered and a Hull Identification Number (HIN) assigned to it. First off, the only way to obtain a legit HIN is to register the ski as a home built vessel and in order to do that it must be a complete vessel. Hull manufacturers are unable to provide a HIN for bare hulls because technically they dont know what will be installed in the hull. At least officially HIN's are also tied to stuff like a vessels motor, HP, seating capacity and other random things. Which is why bare hulls dont come with a HIN. So unless the ski was built by one of the major builders who have the ability to obtain a HIN for a complete build or it was already registered by a previous owner, I'm pretty sure the serial number you references is not a HIN. It might be some serial number from Ricketer but not a HIN.
Couple questions: Are you the first owner and did you build it or have it built?
Assuming you are you need to go to your states DNR website and look into registering a home built vessel. I know when I did mine I had to provide a bill of materials for the vessel, I'm not sure if that's a requirement for your state or not. One thing I will recomend is that you do not tell them that you specifically used a Yamaha Superjet for most of the parts. I did and that only confused them more and resulted in my Rickter XFR being registered as a "Home Built" Yamaha Superjet. Haha I was so frustrated by that point I just let it go and called it a win. I got my Home Built HIN and that's all I cared about. Fyi: I believe that a potion of the HIN they assign you will be common to all home built vessels in your state and thus can be distinguished from non home built vessel HIN's.