Further forms of ijāzah involve an unidentified recipient, someone not yet born, or permission conditional on a future event. Examples include authorizing whomever a named person selects, a future child, or a recipient only if some specified condition occurs.
Some scholars allowed wider use of these forms, while others restricted them. In particular, an unresolved, unknown recipient leaves a substantial uncertainty about whom the authorization actually covered.
The point is not that all ijāzahs are equally clear or equally strong. The authorization's object, recipient, condition, and means of obtaining the written material must each be investigated.