Apparently scribe 3 of 𝓞 dropped the subject pronoun I from this clause beginning with “yea and”. Oliver Cowdery added it when he copied the text into 𝓟. There is evidence that scribe 3 of 𝓞 tended to omit the subject pronoun I, as in the following two examples:
In the first example, scribe 3 of 𝓞 caught his error and supralinearly inserted the I (characteristically spelled by scribe 3 as a lowercase i ). In the second example, his supralinearly inserted i was so weak that Oliver Cowdery apparently missed it when he initially copied the passage from 𝓞 into 𝓟. Later, with heavier ink flow, Oliver supralinearly inserted the I in 𝓟.
In similar clauses beginning with “yea and”, the subject pronoun I is never missing:
Thus both scribal and textual evidence support Oliver Cowdery’s emendation of the text in 1 Nephi 5:8.
Summary: Maintain Oliver Cowdery’s addition of the subject pronoun I in 1 Nephi 5:8 (“yea and I also know of a surety”).