Scribe 3 of 𝓞 wrote “yesterday and today and forever”. In an apparent attempt to delete the first and, scribe 2 of 𝓞 crossed out the day of yesterday as well as the following and, but in correcting for the deleted day, scribe 2 supralinearly inserted to, probably under the influence of the following today. Of course, the resulting text is garbled (“yesterto today and forever”). Oliver Cowdery, when copying into 𝓟, interpreted the text to read “yesterday today and forever”, which is probably what scribe 2 of 𝓞 intended.
Such editing is consistent with usage elsewhere in the text. There are six other occurrences of “yesterday today and forever”, but none of “yesterday and today and forever”:
Interestingly, the corresponding phrase in the King James Bible is indeed “yesterday and today and forever”:
There is another passage in the Book of Mormon text where and is repeated, although this example involves tomorrow rather than yesterday:
So and can be used to separate all three conjuncts of time. Thus the original hand in 𝓞 for 1 Nephi 10:18 (scribe 3’s “yesterday and today and forever”) is perfectly acceptable, even if it is unique for the Book of Mormon.
Summary: Restore the deleted and in 1 Nephi 10:18 (“yesterday and today and forever”); although unique, this reading is supported by the use of “today and tomorrow and forever” in Moroni 10:7.