. . . and when did he come to know it? This reformulates and continues the interesting exchange from the earlier Losing a Lost Tribe post. The question refers to Joseph Smith's apparent knowledge of things Nephite independent of the Book of Mormon text.
Those arguing for the Continental Geography Hypothesis (CGH) cite Joseph Smith's telling of Nephite stories to his family years before he translated the plates (as described by Lucy Mack Smith), the Zelph accounts, other remarks by Joseph Smith, and the traditional understanding of Native Americans as descendants of the Lamanites (memorialized by the current Introduction to the Book of Mormon, which describes Lehi's descendants as "the principal ancestors" of Native Americans). Of course, proponents of the CGH aren't really arguing for a continental geography, they are arguing against historicity.
Those arguing for the Limited Geography Hypothesis (LGH), the view generally advocated by FARMS authors, attempt to downgrade Joseph's extra-textual knowledge of things Nephite and suggest he could, should, or did know nothing more about Nephite origins, history, culture, or extent than is available from the text of the Book of Mormon, regardless of what Joseph himself thought or stated. This is a tricky position to maintain, running counter to traditional Mormon deference to any verifiable statement by Joseph, especially as it concerns the Book of Mormon. Of course, proponents of LGH aren't really as concerned about Nephite geography as they are laboring to maintain a plausible conception of the Book of Mormon as a historical document describing real-world events.
I believe we can advance the debate and peel at least one layer off the misleading geography discussion by asking commentators to directly address a key question that frames their geography arguments: What extra-textual knowledge did Joseph have, and when and how did he obtain it?