Books difficulty levels are relative to other books, and subjective though. Level 30 or 32 have no innate meaning or difference - except as reader perception, relative to the other material graded, gives them one. There’s no rubric they’re based off of either. So if the corpus changes over time, or trends in reading and language learning change, it makes sense that a book’s level would fluctuate somewhat.
(Exactly how sensitive the recency bias should be is a different question tho)
The problem with また、同じ夢を見ていた in particular is that there’s a lot of room for interpretation in the grading. The vocab is basic, it’s the way the sentences are structured and the… strange things happening that make up most of the difficulty. It makes you doubt your own understanding, specifically because it’s unexpected sometimes. So people are bound to continue grading it differently, and thus the level will keep moving in this range.
The other problem is that it’s a common early or first reading choice. So people grading it may be coming from vastly different vantage points/skill sets. Whereas if it were being graded solely by a bunch of people who’ve already read multiple L30s books, you’d expect more consistency (which is not to say it would be any more/less objectively correct)
Except that we do have some fixed level books that are supposed to set the JLPT levels. I have no idea how that works but maybe that’s a part of it too?
I also agree that the most graded books really shouldn’t change their levels, even if it’s only +/-1, but I’m also not that familiar with grading systems so I’m not sure if something else would be better?
Interesting - do you know which ones? Anyway that just means that the levels have a loose correlation, but still no objective difference (at least within their JLPT-correlated tiers). Like the difference btwn L31 & L33 is “ppl perceive an L33 book as a bit harder than the L31 book”
I don’t know which ones, and I really only know about it because they were setting the levels in German and Spanish when those languages got introduced. I don’t see some of the most tenured Natively users around much anymore, but there’s probably someone active who knows/remembers? 
The set ones are textbooks, I think, as obviously they are correlated to the levels that they promise to teach. But don’t ask me which ones.
All of them:
– Our Grading System | Natively
(But I don’t know whether that’s what @shitsurei meant or not.)
Since the German side of the forums is so quiet (
), I was able to grab the thread I remember from back when it was being set up:
I’m assuming a similar set of books are also underpinning Japanese.
Any Nonfiction recommendations?
I’m not sure if I have anything specific in mind but preferably a book that makes you think about it a while after you have read it or alternatively something that you could learn from.
Level 40 seems to be about my current max so something within that would be best.
Are there any taboo topics? I ask because I do enjoy nonfiction but not everyone enjoys things like パパ活女子 幻冬舎新書 | L34 or true crime
なぜ働いていると本が読めなくなるのか | L35 (which has a book club starting on May 25th) - seems like it would fit
nothing taboo, as long as it’s interesting I’m willing to read anything.
@暁のルナ thanks I’ll check it out!
Nonfiction covers quite a lot of ground and you don’t say much about what subject matter you usually read. Here’s some stuff I liked from the nonfiction I’ve read; maybe something here will appeal to you:
ことばの発達の謎を解く | L34 – pop science treatment of language development. Easy read if the subject matter sounds interesting.
暇と退屈の倫理学 | L40 – philosophy for a popular audience, about why we get bored and how we should maybe think about it. Definitely in the “makes you think” category.
増補 日本語が亡びるとき: 英語の世紀の中で | L40 – I liked this one a lot. Book length essay on why Japanese literature had a tremendous flowering in the late 19th and early 20th century as Japanese and Western culture came into contact, and other things. I didn’t always agree with the author but it was always thought provoking. (Longer review on the Natively page.)
日本の解放区を旅する | L40?? – been a long time since I read this, but if you like reportage this author could be worth a try. Their specialty is sympathetic reporting of the lives of people on the losing end of society (they got famous for doing an expose of terrible working conditions in Toyota’s factories, IIRC), and this book of essays has pieces on Brazilians in Japan, Okinawan protestors against US bases, and similar social topics.
零戦 その誕生と栄光の記録 | L39 – an engineer’s view of the Mitsubishi Zero fighter plane as an engineering project (the author was the lead designer).
陰翳礼讃 | L43 – wildcard suggestion since it’s above your level, but if you feel like trying something that’s difficult but where the writing rewards working through it slowly I recommend it. Essays by a famous author. The title piece is a very well known one about the role of shadow and darkness in traditional Japanese culture. There’s also one in there (assuming you buy the book rather than following the Aozora link) about Tanizaki’s favourite toilet experiences 
Edit: I haven’t written reviews for everything non fiction I’ve read, but feel free to ping me here if you want to know what I thought about something that Natively lists me as having read.
WOW! Great recommendations! Will check them out, Thanks! 
It’s gotta be うんちの行方 | L35! Funny, gripping, and it has lived rent free in my head ever since. 
You will learn all kinds of fascinating things, such as the existence of a circular poo economy in the Edo era.
I second なぜ働いていると本が読めなくなるのか | L35, it was a pretty interesting read.
Otherwise, maybe 哲学入門 | L39. As the title implies, it is an introduction to philosophy, but focusing on topics rather than listing the work of previous authors.
Slightly above your max level, but 「江戸」を楽しむ | L41 was interesting too, and introduces a bunch of concepts from the Edo period. That book helped me a lot understanding other books set in that period.
Completely different direction, but I mentioned オカマだけどOLやってます。完全版 | L25 on the forum recently, so why not here too. Autobiographical, a Japanese trans woman talks about her transition.
When I thought of taboo topics this was not on my mind. 
But I’ll take your word for it and give it a try so thanks! 
I was actually looking for an introductory book into philosophy but couldn’t make up my mind so this is perfect. I’ll check them out as well thank you very much! 
