Here in Ether 11:6, 𝓞 is extant for the words “never had been upon the face of the earth”, and it reads without the past participle form known, unlike the virtually identical reading in the next verse (which is not extant in 𝓞): “never had been known upon the face of the earth” (Ether 11:7). Lyle Fletcher suggests (personal communication, 23 September 2004) that in Ether 11:6 the word known was accidentally lost during the dictation of the text. Of course, one could argue, contrariwise, that the known in verse 7 is intrusive and could have been added during the early transmission of the text.
There is one example in 𝓞 where known was initially omitted (but there are no examples in the entire history of the text where known has been accidentally added):
So there is some possibility that known could have been omitted from Ether 11:6.
On the other hand, there is nothing particularly wrong with the earliest reading in Ether 11:6. Note that there are other cases in the text of the verb phrase “never had been”:
(This is in contrast to six instances in the text of the verb phrase “never had been known”, including the one in Ether 11:7.) In Mormon 4:12, listed above, the text could have alternatively read as “and there never had been known so great wickedness”. Since variation can occur, it is more reasonable to accept the possibility that the past participle known is lacking in Ether 11:6 but occurs in Ether 11:7.
Summary: Maintain in Ether 11:6 the phraseology without known (“such an one as never had been upon the face of the earth”) even though in the next verse known occurs in otherwise identical phraseology (“such an one as never had been known upon the face of the earth”).