The 1892 RLDS edition removed the second yea, perhaps because the previous clause began with a yea. The following RLDS edition (in 1908) restored the yea, undoubtedly because the word is in the printer’s manuscript (which was used to edit the text for the 1908 RLDS edition). The phrases “yea then” and “yea and” are found frequently in the text, especially the second one (which was the one that was altered here in 1 Nephi 19:16).
Summary: Maintain in 1 Nephi 19:16 the case of yea and that was changed to and in the 1892 RLDS edition.