We know Hook met Regina for the first time days before the casting of the Curse, but he had obviously been in FTL before then, long enough to learn about Belle.
I think there is still leeway in the timeline for Maleficent to have told Captain Hook about Belle and the dagger. She might have done so in between points 13 and 14. Alternatively, Maleficent could have told Hook between points 15 and 16.
But he didn’t know about the dagger when he confronted Belle, just the rumors of such a weapon. Those pesky details alluded him. So, I think I agree that Mal told Hook about Belle and what she knew about the weapon capable of killing the Dark One but Cora told Hook about the specifics.
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"He was a lot of things to me" "The only conclusion was love"