Maybe only children can’t leave once they set foot in NL. That may not apply to The Dark One.
Also, I think that Jefferson realm jumped to NL when he worked for Rumple.
Maybe he took the pic to PP. And, being that he realm jumped, he wasn’t stuck in NL.
It’s part of a theory I posted on here somewhere a while back about Jefferson writing the book.
He met Bae in NL and knows his story. Jefferson worked for Rumple a could have found out about the dagger, or Jefferson could have also ran into Hook in NL and found out about the dagger from him.
That could also tie in with how August knew about the dagger and who Bae was. August went to SB at least once before we see him arrive in True North (when Regina is talking to Emma in 7:15 am, August rides by and Regina says he looks familiar. Which is odd because August looks a lot different than when he was a child, so why wouldhe look familiar to Regina?). August met with Jefferson. Jefferson is the one who told August about the dagger and Bae and then August went to find Bae as we see in Tallahassee.