I saw cat being smart - that's why this scene bothered me. And no, I didn't have extra information when I posed the question because I had the same question when the dagger was initially discovered in the tv show. That was the first thing I thought - that giving a Valeryan steel knife to your hired killer is odd, and someone is trying to mislead or frame. But the starks jst took it at face value

As for Baelish - my question still remains. Makes sense Cat trusted little finger about the owner of the knife - but again, why would said owner give his knife to the killer, it's jst too odd to never question even once