John Lott page 

Is "only a single" really POV? The point of that sentence is that the claim was an unimportant part of JL's work, until JL made it important by repeating it all the time. Hence, the statement that it appeared in only one sentence in his book...but when you delete the "only," the intention of the sentence becomes unclear. Perhaps "exactly one" or something of the sort would do fine, but just saying that it appears in one sentence is puzzling.