الْخَطُّ مُتَشَابِهٌ، وَالْخَتْمُ مُخْتَلِفٌ.
The handwriting is similar, and the seal is different.
Each clause reports an independent observation. Wāw places the two under a shared inquiry: identifying and attributing the letter. One observation may support an attribution, while the other calls for caution. That common investigative purpose is the pertinent connecting feature (jāmiʿ).
The second clause is neither a substitute nor a mere emphatic restatement of the first. Coordination does not itself assert that the two pieces of evidence have equal force; it presents them together as related judgments.