Weird question about Crests

I'm trying to do a few playthroughs before FW to make sure I know all of the lore in Three Houses, but there's a question that I'm not sure the game will answer, so I wanted to ask here.

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What are the confirmed in-universe effects of the different Crests?

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Obviously, in terms of gameplay, each crest has a chance to slightly alter combat or actions in some way, but I'm curious about what abilities they provide to the characters in-universe.

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I've heard a theory that the Crest of Lamine allows someone to smell blood, based on some dialogue from Jeritza. And I assume Hapi's summoning ability is related to her crest, but I don't know for sure.

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And some crest-users have an extended lifespan. Is that something that all crest-users get, or is that more specific?

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Does anyone have any other ideas to what in-universe boons Crests could provide?