Are you the same Richard Gray?

Kim Cameron summarises some thoughtful comments from Richard Gray on identity and authorisation spread over Jon Udell's blog and Kim's own. Richard notes on Jon Udell's blog:

As you don’t have CardSpace enabled here, you can’t actually verify that I am the said same Richard from Kim’s blog.

But without Kim's co-operation Jon could not verify that the same Richard, presented the same or equivalent credentials using Cardspace. A third party would require co-operation from both Jon and Kim to verify that it was the same Mr Gray. This appears to be the case even if he used the same managed card from an Id Provider trusted by all the parties.
I think we need to explore this use-case further.