Before 1279, during 1279 and after 1279, Nichiren inscribed various gohonzons wherein his name is written immediately under the daimoku, in larger kanji.  In other gohonzons, his name is off to the side, and his kao (flower signature) is of varying sizes.  Both types of gohonzons exists all throughout Nichiren life.  The year, 1279, does not create a delineating watermark.

If not for Yamanaka's work, Taisekiji could make such a
claim and it would have been hard to verify it.  A picture
is worth a thousand words.  125+pictures of authentic
Nichiren gohonzons speak volumes.

Why did Nichikan and other Taisekiji priests add the extra
text about "head split in seven pieces for those who oppose
it" and "100% merit for those who uphold it"? (paraphrased here).  These kanji do not exist on any of Nichiren's Authentic gohonzons, and they don't appear on the one photo of the so-called "Ita Mandara".  These phrases are completely out of context for the setting of the "assembly in the open sky" (ceremony in the air), though these phrases do appear in other chapters of the Lotus Sutra.

Since Nichiren did not see fit to include them in his
gohonzons, why do the Taisekiji priests assume that it's OK to add them?