> I suppose we’re really talking about having an anxiety disorder that impedes the ability to deliver vs feeling anxious on the day. The former should manifest noticeably somehow, by definition.
I'm not really sure what you mean. First, anxiety is on a continuum, so I wouldn't propose a dichotomy here. Second, lots of people have situational anxiety, which I wouldn't call a "disorder". For example, a great fear of public speaking is pretty common.
Of course poor performance at some specific task, e.g., an interview or a speech, is manifestly noticeable, but the cause of that poor performance isn't necessarily manifestly noticeable. In other words, you can't necessarily tell whether it was caused by a lack of skill or competence or just temporary anxiety. Or maybe lack of sleep the night before.
