Your library holds a strong method statement from a hospital refurbishment, and the rate card priced for that client. A writer on a new tender asks the model to draft from it. The method statement reaches the model as it is; the client name and day rate columns you marked on the rate card reach it as placeholders. If that writer is not cleared for day rates and asks for them, the request is refused, and the refusal is recorded.
Fields you mark sensitive reach the AI model masked with placeholders; fields you don't mark reach it as they are. The same value always gets the same placeholder, so masked data can still be linked to a person and remains personal data.
On records loaded into Kovac, someone not cleared for a column you have marked who asks for it is refused, and the refusal is recorded.
Clearance decides what a person may read. It never unmasks a field for the AI model: a marked field reaches the model masked on every call, whoever asks.