Oliver Cowdery accidentally misread 𝓞 when he copied from 𝓞 into 𝓟, and he ended up replacing behold with before. The use of before didn’t create a completely nonsensical reading; one can interpret before as an adverb meaning ‘before this time’. Yet before is otherwise not used like this in the Book of Mormon. Usually, before acts as either a preposition or a subordinate conjunction (that is, before usually takes a complement). When before acts alone as a one-word adverbial, either it modifies the main verb in the clause (such as in 1 Nephi 8:11, “above all that I ever had before tasted”) or, in one instance, it acts as a predicate adverb (in an Isaiah quote in 2 Nephi 19:12, “the Syrians before and the Philistines behind”).
This error of before for behold in 1 Nephi 22:4 was not caught until the 1837 (second) edition was produced. As far as we can tell, the original manuscript was not used to restore readings for the 1837 edition, so the restoration of the original behold here seems to be Joseph Smith’s own emendation to the text, which turns out to be the correct reading. In nearly all of his changes to the text for the second and third editions, Joseph did not restore readings found uniquely in 𝓞 unless he actually checked the original manuscript. We have specific evidence for Joseph using 𝓞, but only in his editing for the 1840 (third) edition. For the few cases where the 1837 edition restores a unique reading in 𝓞, the incorrect reading is sufficiently difficult that it invites a more reasonable reading, as here in 1 Nephi 22:4.
Summary: Maintain the reading of 𝓞 in 1 Nephi 22:4 (“and behold there are many which are already lost”); the change of behold to before is a simple visual misreading and was corrected by Joseph Smith for the 1837 edition, but apparently without reference to 𝓞.