هَذِهِ الرِّسَالَةُ لِلْقَاضِي قَطْعًا.
This letter certainly belongs to the judge.
تُشْبِهُ هَذِهِ الرِّسَالَةُ رَسَائِلَ الْقَاضِي، وَلَكِنْ لَمْ تَثْبُتْ نِسْبَتُهَا إِلَيْهِ.
The letter resembles the judge's correspondence, but its attribution to him is unproven.
The revision separates an observed resemblance from a conclusion about authorship. Wa-lākin prevents an immediate leap from resemblance to certainty, whereas qaṭʿan intensifies the unsupported attribution in the first version. The better expression fits the degree of judgment, the evidence available and the listener's concern to one another.