How could Nephi quote a later Isaiah?

The mention of Cyrus settles it for me. Prophecy can name people before they are born.

That explains why some readers accept earlier authorship. Scholars also consider the audience, the language, and the focus on returning from Babylon. Take the full case seriously.

I see why the setting points to the exile. I believe prophecy can look ahead. Which details tell us when these specific passages were written?

You grant the historical case and make the disagreement concrete. A belief in prophecy can coexist with careful dating of a text.

The date of the finished book leaves room for earlier material. We still need evidence about which words Nephi quotes and what the English translation can tell us about them.

You separate two things we can investigate. One is the age of the Hebrew material. The other is what the English Book of Mormon reveals about the text Nephi had.

If there was any older Isaiah material, these chapters could have been on the plates, so I think that answers it.

The possibility of an earlier source deserves a hearing. To explain the quotations, that model needs evidence that the relevant material existed early enough.

A Church guide says Nephi drew on the brass plates. Latter-day Saint scholars offer different ways to explain the dating question. I would distinguish those models from what the guide teaches.

That answers the question directly. It distinguishes the traditional account from scholarly attempts to explain the evidence and leaves room for further investigation.

BYU scholars have written about expansion during translation, so that is the Church’s explanation.

A scholar’s proposal is evidence of a Latter-day Saint approach. The Church study guide teaches that Nephi drew from the brass plates and leaves the composition dates unaddressed.