There are two ways to interpret the earliest text here in 1 Nephi 1:14. One is that “had read and saw” is a conjoining of the past perfect had read and the simple past-tense saw. The RLDS text has retained the original text here, which presumes that the RLDS editors have interpreted “had read and saw” in this way.
The other possibility is to interpret “had read and saw” as a conjunction of “had read” and “had saw”, with ellipsis of the repeated had. Of course, “had saw” is ungrammatical in standard English, yet this kind of construction was actually quite common in the original text:
For further discussion plus a listing of all the examples, see past participle in volume 3.
It would appear that the editors for the 1920 edition corrected the text under this second interpretation, thus making sure that both main verbs were past participles. Such editing is consistent with all other conjuncts of heard and seen in the original text:
None of these passages show any earlier form involving saw rather than seen. Nonetheless, there is one occurrence of past participial saw in the earliest text:
The 1830 typesetter edited the text to “had seen”, and Joseph Smith also marked the change in his editing of the printer’s manuscript for the 1837 edition. But originally Oliver Cowdery wrote “had saw” in the printer’s manuscript.
Summary: Despite their ungrammaticality in today’s standard English, the original past participial forms of the earliest textual sources belong in the original text, including those forms found in conjuncts of verb phrases.