Joseph,
You are right about the fact that it is more difficult to spot fake Jerry’s Nugget with a sealed box.
But as I have made a nice page with (as far as i know) all ways to spot copies, we have some ways to do it. And I have never seen (or heard of) fake ones that copy all details of real decks
My page :
The stamp tip #23 (even if Lee Asher doesn’t really agree with me) is for me the best way to be sure it is true.