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This is a weird one and I don’t really have a good implementation idea that’s not clunky, but similar to how there are some furigana editions of books, there are ‘modernized’ editions of old Japanese text which update the kanji, and - depending on how old - sometimes even the kana usage and grammar. This will impact how hard it is for learners to read, and thus their grading.
I was reminded of it talking yesterday about how my copy of 黄金仮面 | L38 has updated text (I know because I have the audiobook which is based on the original and there’s noticeable differences) and I saw a review just now of こころ which commented on the modern edition not being as difficult as the current rating.
The tricky thing is that people might not realize they’re reading a modernized version and simply think the given rating is too high.
As a quick example for those not familiar, these are the types of changes I mean:
此処 → ここ
迄 → まで
之 → これ
相違ない → 違いない (different word entirely)
といふ → という
ゑ → え