I do think that Bae is Neal.
but I think that the information about the dagger and Baelfire comes from the Blue Fairy. August was by her and she knew about Baelfire, because she was the one who send him to a land without magic and she is also a very powerful magic being, so she will know everything about the dark one.
I think that August didn’t know or didn’t find out, that Neal is Bae. He said that Neal is only captured in the “Crossfire”, so whatever was in the box, would a normal living person believe in magic. I believe too that the word “Crossfire” is a hint from K&H that he is Baelfire.
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Heros don't get their Happy Ending!