Vaalintine
Wild Wondorous Wolfalope
There IS an exception to that. A Primordial can choose to teach charms to a single exalt and no others. However this comes with the drawback that the charms cannot be learned on one's own, and would require either a 3rd circle tutor or a Yozi forcably cramming them into your head.To clarify my position, as per the book when a Yozi opens the door aka allows a Infernal to use their charms, ALL the infernals get it without exceptions. The 5 Reclamation Yozi have already opened their charms to the Infernals and all of them regardless of Caste have access to those charms. Just at an extra 2xp price if it isn't caste or favored.
Infact the 5 Yozi, well 4 since Adorjan didn't really join in on this, tried to get the others to pen their charms to the Infernals as well, citing a number of benifits like preserving power incase of Fetitch Death and others. So far they have only convinced Kimbery but a few were considering it like Isodorus and Sorzeny.
The infernal sig characters also have multiple charms from multiple Yozi. The book also clarifies that once the door is open it cannot be closed and if it is granted to one infernal all infernal gets it.
Green Sun Princes work differently. Once a Yozi personally
teaches any of its Charms to one of Hell's Chosen, the
door opens for all Green Sun Princes to learn any of that
Yozi's Charms, even without a teacher. Once opened, this
door can't be closed, which is a major source of reluctance
from the Yozis who have not yet decided to take part in the
Green Sun Prince initiative. Infernals can't learn Charms
for Yozis they can't access or Charms one Yozi adapted from
study of a sibling, even if taught by someone who knows the
Charm. Fiends are an exception and may learn the Charms of
prohibited Yozis as foreign Charms using their anima power,
though this does not unlock that Yozi's Charms for all Green
Sun Princes. They can teach Infernal Charms to anyone capable
of learning them and cannot learn the Charms of other
beings except through effects like the Fiend anima power.
Example: Szoreny opens his charmset and has an Infernal running about doing crap. Said Infernal decides to go ask Isidoros to teach him his charms, whereupon the Black Boar says "HOLY SHIT A TINY FOREST!" and accidentally punts the exalt across malfeas. Said exalt wakes up later knowing how to punt people several miles.
This is just a rough example, so I might be a little off on the mechanics due to not having the book in front of me.