It's all built up already so I probably won't have the tubes out for awhile for another picture. I do not believe the valve is replaceable though, it seemed permanent and identical to other tubes I've used that have this same 'threaded all the way down' stem and they didn't come with this washer.
I ordered two of them and both came this way. Closer look at the flatlandfuel picture and the picture shows the same - a conical washer and a nut.
it makes sense to me to be B
That was my original thought as the washer is rounded so no sharp edges and shaped conical so it kinda fits that way well. Seems odd though, you would think they would make it out of something like rubber if that is where they intended it to be placed.
I ended up doing it like A just because they are new rims and so hopefully the washer will provide some protection from the nut scratching then when it's tightened. If anyone does know for sure though let us know.