No it wasn't written anywhere. Their knowledge is extremely localized to where they were and passed through, mostly just a bit of the southwest parts of the Tokyo area. They were contracted after the original groups that caused this whole mess had largely fallen apart so won't know more than rumors about how it started.
Oh, less specifics, and more... universal survival tips.
E.g.: If you see the sun or moon start to flicker,
run like fuck two level 3s are in the area. Demons are drawn to tourists, stay out of the ritzier area; or demons are drawn to despair, stay out of the ghetto; you say that your girl Kaoru can make music that can slow the despair process? BRING EM' AND POP EM' LIKE ADVIL (you don't drink her magic-)
idgaf AD.VIL.
That sort of thing.
For instance this one would be basically what your clairvoyants can already do, except physically crippled on top of it.
Plus super hearing would probably need to be a fair bit stronger than it sounds to match a standard clairvoyant package.
I want to showcase how 'weak' magic can turn out to be super useful once there's more of a tech base or if people get creative with it. You don't
need to be an elite to contribute. For example, super hearing? Maybe it doesn't trigger a clairvoyant headache when used from an anchor (but it has the usual super hearing drawbacks - i.e. you have super hearing and OW THAT WAS A BIG BOOM). At higher levels of specialization you start to be able to do other stuff with it - daredevil-like echolocation, the magical equivalent of perfect pitch, an instinctive understanding of what kind of magic is being used just by the sound it's making. Turn that spell into magitech and you've got a fairly sophisticated ability to 'measure' magic.
(does Keiko have magic yet. I kind of want this to be Keiko's magic now - she was always embarrassed by how weak it was and never mentioned it, but
whoops turns out it can be useful TIME TO SCIENCE THIS)
As for the astral projection - the advantage that comes to mind is an ability to remotely trigger spell anchors, something clairvoyants should not be able to do. She's the one that can act as a backup, that can hit the healing anchor on an unconscious puella, or the barrier anchor for one that's being distracted by something else. The no heal-clause is admittedly a bit gratuitous, but I hope it'd be an interesting character arc. She starts off as being her group's eyes and ears, but when she joins the Serene group she realizes others can do it better than she can - it's like her legs all over again, she's being held back again, she's useless (she doesn't want to be useless, she was abandoned once before, if she's abandoned again...) - until she discovers no, wait, she
can do something no one else can do.
And so on and so forth, hoho.