The title is a reference to No One Knows What Science Doesn’t Know, from which I infer that it’s supposed to be read as “There is some set {what PA knows}. No one can know exactly where the boundaries of this set are.”, not “There is some set {what PA knows}. No one can know the truth value of any proposition not in this set.”.
The title is a reference to No One Knows What Science Doesn’t Know, from which I infer that it’s supposed to be read as “There is some set {what PA knows}. No one can know exactly where the boundaries of this set are.”, not “There is some set {what PA knows}. No one can know the truth value of any proposition not in this set.”.