Some things for the English speaker to know what Nichiren actually taught

Knowing the truth of what Nichiren actually said is complicated by translations with a certain sects bent; whether or not they use the Gosho Zenshu, or gosho collection written in the modern Japanese and translations as the SGI or a Nichiren Shoshu, or whether they utilize the original collections of the writings, the Showa Tehon collection which all scholars and scholar priests utilize. Even here, the English translations may have a Nichiren Shu bent (therefore, one would do well to read all the available translations, if possible and especially, the five Major Writings); and lastly, the problem with apochrypha or pious forgeries. The very best article in English was Dr. Jacqueline Stone of Princeton PHD dissertation, Some disputed writings in the Nichiren corpus: Textual, hermeneutical and historical problems." University of California, Los Angeles, 1990. Dr stone also was the principle translator for the SGI Writings of Nichiren Daishonin. She admitted later that her SGI translation was not equal to academic standards, ie: They were based in the modern Gosho Zenshu and not the Showa Tehon. 

The Showa Tehon has several parts: the Gosho definitely in Nichiren's hand and colophon; those probably in Nichiren's hand (in complete agreement with the corpus in Nichiren's hand, appropriate for the time period in which Nichiren wrote, and Nichiren's sentence structure and syntax, as determined by computer analysis, matched Nichiren's writings and were discovered early; Gosho probably not authentic, those having different structure and syntax and the teachings/principles are not in accord with the evolution of Nichiren's thought, and they were discovered late; and those definitely not authentic writings, like the Ongi Kuden and The True Aspect of all Phenomena (some parts added to the Shoho Jisso Sho), Conversations Between a Sage and an Unenlightened Man and dozens of others. Those definitely not authentic writings may have incidents that Nichiren reported that occurred after he died and all the other anomalies sighted above.

There are several lists of the authentic/inauthentic writings. The one I use principally is http://www.kempon.net/authentic%20writings.html

Jacqueline Stone's dissertation: https://www.princeton.edu/~jstone/dissertation.html

A lot to digest, I know. but to know what Nichiren actually taught, these principles are important to accurately ascertain what really are The Three Great Secret Laws and the Three Treasures of Nichiren Lotus Sutra Buddhism. Of course, the illiterate Atsuhara martyrs knew nothing of the above, they only chanted the Daimoku. However, todays disciples and believers are almost all literate.