Nonsense. Of course you know what you experienced -- after all -- you experienced it.
As an agnostic, you just don't have a vocabulary to describe it adequately.
That can be easily remedied.
Made sense to me
. ...and still does
. Maybe if I rephrase it you'll see what I'm trying to say.
I don't know the ultimate nature of any of my experiences. As such i don't "ultimately know" them. People every day have experiences they'll understand better another day. They don't have ultimate/complete knowledge of those experiences even as they initially experience them.
As an agnostic I think it likely the ultimate nature of the universe is incomprehensible. If indeed it is incomprehensible I'm not sure how vocabulary could apply.