Continuing the speculation on fibre and materials (my beloved)? resource scarcity, tradition, and the ninth….
Let’s talk about how the ninth might use their hair.
Harrow keeps her hair shorn and I believe had parents do as well. I will say that as the religious leaders of the congregation they might follow a slightly stricter version of the rules. (It’s implied that wearing face paint 24/7 is more of a harrow thing and people don’t really wear it when they’re at home)
either way, the ninth tries to live as resourceful efficiently as possible and people are constantly creating hair.
If everyone shaves their head semi regularly then the hair would probably be short enough that it’s be used for stuff starting fires. If they had enough of it they could try to use it for stuffing objects like pillows, (rare but does happen)
my other idea based on the fact that the ninth is morbid, and their clothes seem pretty complicated, harrow specifically has a lot of jewelry and buttons and lace… maybe they use their hair for decoration. In the Victorian era people used to make jewelry out of their hair. It would be resource efficient, morbid, connect you to the dead, and pretty.
Also think of this… knuckle bone prayer beads made from an ancestors bones with their hair as the cord.
I dunno maybe they would grow their hair out specifically for the purpose of using it. I feel like that’d be a good exemption.