The printer’s manuscript has “yea even until”, but the 1830 edition lacks the yea. The 1908 RLDS edition restored the yea to the RLDS text, but the LDS text has maintained the 1830 reading without the yea. Here it seems that the 1830 compositor accidentally omitted the yea.
Typically, the phrase even until is not preceded by a yea, but there are two occurrences elsewhere in the text of “yea even until” and they both occur in the same passage:
Excluding the case here in 3 Nephi 3:8, in the original text there are 48 occurrences of even until without a preceding yea. (For one case where even until is probably an error for even unto, see under Mosiah 17:10.)
We note here in 3 Nephi 3:8 that the previous clause ends in the pronoun you (in the phrase “and shall let fall the sword upon you”), which looks very much like yea. We have already seen examples where yea has dropped out of the text when immediately preceded by you. In fact, in two cases the following word was even, just like here in 3 Nephi 3:8:
But in these two cases, the loss of yea occurred when Oliver Cowdery copied from 𝓞 into 𝓟. Moreover, in each case, Oliver initially omitted the you in 𝓞, which seems to have led to difficulty in copying the following yea into 𝓟. Here in 3 Nephi 3:8, on the other hand, we have a case where the 1830 compositor would be responsible for the omission of yea. Even so, the immediately preceding you is visually similar to yea and could have led to the omission of the yea.
Elsewhere in the early transmission of the text, there is one instance where Oliver Cowdery accidentally added a yea:
But there is also one instance where the 1830 compositor omitted the yea:
So here in 3 Nephi 3:8, Oliver could have added a yea or the 1830 compositor could have omitted the yea. More generally, however, the tendency in the transmission of the text is to omit small words rather than to add them. For instance, if we count all clear cases in the transmission of the Book of Mormon where yea has been accidentally omitted from the text or added to it, there are six instances of omission but only one of addition. (In this count, I ignore all instances of momentary error in the manuscripts as well as four cases of conscious editing by Joseph Smith, although nearly all these changes also involve the deletion of the yea.) Thus here in 3 Nephi 3:8, the critical text will accept the reading of 𝓟 with the yea. See volume 3 for a complete discussion of the more prevalent tendency to accidentally omit words rather than add them.
Summary: Restore in 3 Nephi 3:8 the yea before even until, the reading of the printer’s manuscript and the much less frequent reading in the text; the 1830 compositor probably accidentally dropped the yea when he set the type from the original manuscript, perhaps because the preceding you looks like yea.