How do they realize they are sorcerers? How do they figure out what spells they have? (Especially given that the player can choose the spells that have no relation to the source of the sorcerer's power?) It's the sort of thing that is seldom role-played. And what with verbal, somatic, and material components, it is hard to see how it can happen accidentally.
Even in Gamelit, that tends to be the point at which characters breaking the fourth wall and start talking about choosing spells. It might work in some Gamelit worlds, but the language used would sound different.
But in this world, a sorcerer who does not use the magic regularly will find that it -- uses itself. Particularly if the sorcerer is angry (for offensive spells) or frightened (for defensive and stealth ones) and possibly excited (for dramatic ones), but that will merely accelerate what happens naturally. Different types of sorcerer are differentiated by the spells they spontaneously cast, not by changes to appearance and the like.
Without verbal, somatic, or material components, of course. Those are introduced in order to let the sorcerer get some control. And then maybe the sorcerer picks up metamagic feats to let him do with more difficulty what he did before he learned the components. But with more control.
It's no wonder that it's the law in this world that sorcerers have to go adventure. Even if reverse engineering what they do is a major source of spellcraft for others who cast spells. (Though to be sure picking up more spells while adventuring increases the odds that someone will want to reverse engineer one. Or several.)