I took my XR650R title down to my local Licensing business and tried to get the same thing done. Problem was she was familiar with the official state policy. She asked if the state patrol looked the bike over. I told her they would not inspect any bikes for this purpose anymore but that it was still legal to issue a dual purpose license. So she got on her computer and started looking up the requirements for dual purpose licensing. I was watching her screen and according to everything she was reading she could do it. She couldn't believe what she was reading so she called Olympia. They told her no and so she said she could not do it.
In the end their computers have to agree with the present law that actually allows dual sporting. But the official policy does not have to agree with the law. I suspect after all your paper work gets to Olympia they will see that the lady who helped you broke official policy. She will be reprimanded for her actions and will not do it again.
I noticed in your pictures that your bike is not street legal. So you better be careful. The plate will not save you from a ticket if you do not have brake lights, horn, mirrors and speedometer which is a bare minimum for riding on Washington State roads including logging roads.
I'm glad you got your plate, I may try a few more places but over here they are pretty familiar with this issue.
So you're claiming that the "official" policy of WA is that you can't get it plated? If that's the case, why would the computer tell her differently? Are you sure it wasn't an ignorant, under achieving, over paid employee in Olympia?
Since you're trying to get your's plated, it seems to me that you should talk to this guy and bring the DMV Woman a box of chocolates and tell her ImpalaR1 sent you!