Yes I assume about as much as you do unless you actually work for them? The seller doesn't control the registration system and thus cannot authorize a license. I know it's probably not the way it probably works, but if NI is made aware that a legal sale of the software occurred, then since it's in their own legal agreement they should transfer it with proof.
I know in the real world that's not how the legal department might look at it, but I'm just saying from the practical point of allowing them to be transferred in the first place. If it were advertised as complete, or coming with the software, I'd try and press the issue.
You're right about the last part. It would seem to me that if they are made aware of it then the software license would no longer be valid.