Here the 1905 LDS edition accidentally omitted all from the phrase “upon all the face of the land”; the 1911 LDS edition also lacks the all (its copytext was one of the later printings of the 1905 edition). The 1920 LDS edition restored the all to the LDS text. Either reading, with or without the all, is possible. Elsewhere the text has 23 instances of “all the face of the land” and 39 of “the face of the land”. See under Helaman 14:20 for a general discussion regarding the textual variants for the phrase “the face of the land”. For each instance of this phrase, the critical text will follow the earliest reading. For another example of the omission of all from this phrase, see nearby under Ether 13:31. In that case, the 1840 edition accidentally omitted the all.
Summary: Maintain in Ether 13:26 the all in the phrase “upon all the face of the land”, the reading of the earliest extant source (in this case, the printer’s manuscript).