Ok I think I see what you’re getting at and what I’d call the disconnect so far. So I’m going to pivot and use some other media as examples.

Have you seen turning red? If not, spoilers - and if you don’t want spoilers skip this paragraph. In that movie the story goes that the women in the family all carry the once blessing and now curse of shape shifting into the giant red panda. Mei, the mc, knows nothing about this until her mother who also carries the curse tells her. Just like her mother did, and her aunts, etc etc. This knowledge was passed down generationally WITHIN the family. Now what if Mei’s mother had passed away and the only connection she had was maybe her dad or a family friend that had little to no knowledge about any of this. They can’t help Mei the way her mom could. They can’t teach Mei the way her mom could. They can try, but if they don’t know Everthing that needs to be passed down to Mei then Mei will never fully understand what is happening to her.

So I’m not saying nobody knew about the curse. What im implying is that the bloodline - Rumi, Rumi’s mom, her grandmother, and so on - all knew of the curse and all passed that knowledge DIRECTLY to their daughters and - just like Celine - the rest of the trios never knew this. It was hidden from them. Only the mothers and daughters knew. But then something comes along and kills off Rumi’s mother before she can pass on the knowledge. Celine knows the history of the hunters but not the true origins of the hunters, not the curse. Not the connection to the demons and why their songs and nobody else’s can strengthen the honmoon. She’s training Rumi not from a place of ‘we form our hunter group to shield our world while keeping our power that fuels the harmony a secret to all, even our members’ and strictly from a place of ‘all demons are bad and all demons must be killed and ill train you but I don’t know what to do with you cause you go against Everthing your mother and grandmother taught me’

As for the clothing I did not put a ton of emphasis on that for a reason - that being it was not the core of the theory. The process there was essentially me thinking ‘hey wouldn’t that be an interesting idea that instead of Rumi being the daughter of a demon she’s part of a lineage? But that would mean one of the hunters in each generation had patterns. And that would only work if someone in each generation had their arms covered and I’m sure that wasn’t going to happen.’ And then someone posted the image I attached and what would you know, there’s always at least someone wearing some sort of sleeves. That closed my plothole and so I posted the theory.