Meridian Magazine has an excellent set of quotes dating back to the 1920s — including from Church publications and General Authorities speaking in General Conference — cautioning members (e.g.)
against the error of supposing that all the American Indians are the descendants of Lehi, Mulek, and their companions, and that their languages and dialects, their social organizations, religious conceptions and practices, traditions, etc., are all traceable to those Hebrew sources. [from a Book of Mormon study guide, 1927]
These quotes, in turn, are taken from the FAIR Wiki article on the same topic (which, unlike the Meridian article, has detailed citations).
This issue remains important, because I still see a few commenters in the Bloggernacle claiming that the limited geographical model of the Book of Mormon, as well as the recognition that not all Native Americans descend from Lehites and Jaredites, are “late” (i.e., recent) responses to mainstream archeological and genetic (DNA) research of the past few decades. That’s just not true. Limited geographical models started before 1920, with Willard Young (son of Brigham Young) proposing a Mesoamerica-only geography of the Book of Mormon, complete with the Hill Cumorah in Guatemala) sometime before 1920, while Louis Edward Hills (of the RLDS Church) proposed a Central Amercia/Mexico-only model (with Cumorah in central Mexico) in 1917.
Likewise, the Meridian article and the FAIR Wiki article from which it draws make it clear that Church materials and leaders were anything but unanimous in claiming Native Americans all descended from Book of Mormon peoples. I’ve previously cited from Hugh Nibley’s writings in the Improvement Era (the Church’s official magazine and precursor to the Ensign) back in the early 1950s, but these new quotes go back a generation earlier. ..bruce..