Perhaps I'm indeed underestimating the misconception of occultless mortals in areas with strong Immaculate propaganda.
No.
Any mortals, and most Exalts. Creation is fallen. Knowledge is lost. Unless you are a specific expert in the field of demonology, you will not know much about the Demon Realm - and if you are an expert, you damn well better justify it with your background because that is not common knowledge and neither gods nor most polities want people outside their control just summoning demons.
Because studying demons means you will, inevitably, learn how easy it is to beckon demons.
Beckon (Demon Species) only requires Occult 3 - that's Occult 2 and a Speciality in "Demonology". Any learned occultist can learn how to summon a kind of demon if they just study the field and find the spell in question. Which means that the knowledge has to be controlled, or people will unleash unbound demons on Creation. If you're lucky, they'll be a stupid demon who'll eat their summoner. If you're unlucky, they'll be a smart demon who will come to an arrangement with their beckoner because that gives them a way out of Malfeas whenever they want it - and suddenly you've got a brand new demon cult with a First Circle backing it, which can go toe to toe with small divine cults.
That's why knowledge on demons has to be controlled in Creation. Because it's easy to unleash First Circles on the world with the level of knowledge you need to recognise First Circles.
For example, let's take the typical mortal of Great Forks (because I'm playing a Great Forker and so read up on the city). The city has Occult 3 and +3 Supernatural Etiquette on top of it, and is renown for its universities and libraries (and literate citizens). This means that the professors (whatever you call them in Exalted) know their barzinoi from their barzinai and their shimei from their shin giri - and these sorts of savoir-faire involve quite some understanding of the soul hierarchies and respective characteristics of its members.
The Creation Ruling Mandate system is terrible and I afford it no respect at all. Basing your argument on that is laughable. No, it's
stupid to give the typical mortal of Great Forks Occult 3 and a +3 speciality.
Yes, Great Forks as a city as a whole probably has some occultists in it which have more knowledge about demons. Not the average peasant. And even the occultists will probably have the knowledge in the style of Mediaeval occultists. Which is to say, they'll have read books which say things like:
"The demons that dwell in the Demon Sea that is called Kaimbery, Kimmberry, or Kimberlei by the damned are split into two kinds. Those which assume a male aspect are called the barzinoi, while those which assume a female aspect are called the barzinai. Some demon breeds exist within both the barzinoi and the barzinai, but others exist only within one. Few demon princes that dwell within the sea possess both male and female aspects, and it is believed that the toxic waters of the Hellish Ocean hate the conflation of aspects. This is related to the way that the magical acid vitriol - from which the sea is made - reduces all things to their base state."
After all, mediaeval monks obsessed about demonic hierarchies and ranks and populated things like the Ars Goetia with knowledge. In fact, the demonology textbooks of Great Forks probably resemble this
page on the Ars Goetia.
Hell, something like this could basically be ported straight in:
Leraje (also Leraie, Leraikha, Leraye, Loray, Oray) is a mighty Great Marquis of Hell who has thirty legions of demons under his power. He causes great battles and disputes, and makes gangrene wounds caused by arrows.
He is depicted as a gallant and handsome archer clad in green, carrying a bow and quiver.
But this isn't some great thing of metaphysics. These are books on specific demons and observed phenomena. Great Forks does not have the knowledge of the High First Age, and it's specialised, localised, and not common even there.
And Exalts are in an even better position than that: they also lack the penalties for not having dots in a skill, so they can intuit things that they haven't been directly taught.
Nope. I strongly disagree. I absolutely reject the idea that the map is the territory, and I would not let a character who has not been in the position to study demonology to "just intuit" things about the Demon Realm to that detail. They'll be able to work out some things - but they'll be the insights of a prodigy on the evidence of their senses, not learned knowledge.
To put it another way, if your Occult 4 Eastern shaman who knows all about the spirits of the Eastern woods and the elementals and fae who stalk this place started asking questions about how the circles of demons work, I'd give things like "Demons are divided by power. The lowest demons are weak things akin to the lesser elementals, but the mightiest are said to be even more powerful than the gods" and "Some say that the demon realm approaches the mortal world during Calibration". Which are astute observations he might have come across or put together from things he's seen in Calibration.
He'd actually need to put work into learning about demons before he got more. Skills cannot pull knowledge from nowhere.