أَهِيَ لِلْقَاضِي أَمْ لِكَاتِبِهِ؟
Is it the judge's or his secretary's?
The interrogative hamza and am present two specific alternatives. The questioner seeks a decision between competing attributions, not merely confirmation that a letter exists. Repeating wujidat risālatun would miss the question's actual focus.
Where neither attribution has been established, an appropriate response is لَمْ تَثْبُتْ نِسْبَتُهَا بَعْدُ — its attribution has not yet been established. This does not invent a third attribution; it withholds judgment on the alternatives until evidence is sufficient.