@Susan, thanks for the invite. Since you are familiar with the source below, can you clarify what differentiation the author is making?
The NT...contexts of "Isaiah" may be perfectly well understood as a reference to the book, not the author. The only passage where the prophet himself is involved in action rather than as speaker or author in the argument is at John 12:41 ("Isaiah said this because he saw his glory and spoke about him [NRSV]") [emphasis added]
IVP Dictionary of the Old Testament: Prophets [p370-371](https://books.google.com/books?id=w50mDAAAQBAJ&lpg=PR1&pg=PA370#v=onepage…