Oops, I meant to make that more absolute; is it metagaming to claim scribe note evidence as undeniable proof? That is, if the attacker isn't ID'd, but is game mechanically obvious, would our characters take it as obvious as well?
I understand that this will ultimately fall to how the characters play it, but is it right to get fed up (IC) when someone tries to deny this kind of proof? Or should we (potentially) accept the RP description?
The scribe note is undeniable proof that the noble is there.
It is not undeniable proof—either IC or OOC—that they are the ones who did the deed. (Unless they're the only noble in the region, and there's no way another noble could have gotten out of there in the meantime.)