I don't remember it stating that.
There you go
Well, it says in the start they used Daizenshu and other things, so when it's not clear in material, they just state their theory in wordbox.
...or they don't? Where was it stated that people in Dragon Ball "manipulate the E=MC^2 formula perfectly so they can create massless spaceships that travel at SoL" literally anywhere else but in that book?
Hell, even if we go by your logic that the main source of the book is Daizenshuu and all other already-existent databooks... then more reason to not consider it canon, because it's just retelling what you either see happen on the work or is told in the Daizenshuu. I.e., their veracity only goes as far as the information they are claiming comes from the work/the Daizenshuu. So, directly looking at the original source of information rather than a book who only tells you the interpretation a certain person gave to what he found on the Databook is always more reliable. And, given they have stated to fix the gaps not stated with whatever is on their mind several times, then everything not in already well known databooks is meaningless because it can perfectly be a headcanon, like several "a guess here and there" or "ok, Toriyama didn't say this but we think it works this way" claims.
I read all 3 of them, but I can't remember statements like that
Refer to the previous imgur link
Maybe for d&d like thing? In the guide they clearly state that Bulma is ordinary human, but in-game content they gave her some big stats.
I doubt changing the word "match" for "c" will cause too many problems in a d&d game.
Well, Daizenshu states the same about PL, but we don't say that it's not canon because of it.
The difference is, Daizenshuu is not constantly written in a hypothetical tone. It states how things work, does not make theories and fills the gaps with the person's headcanon. Doesn't say "Toriyama didn't explain this", because they are the Word of God. They are explaining how things work in canon, not a summary of what Toriyama said or didn't say.
And thing with 150m and 15m can be just a typing mistake, since in Daizenshu 150M PL was written with kanji this way it can be mistaken for 15M(this type of sht happenes even in official dub, I remember in Russian dub of Spider-man 1994 many such mistakes(Yeah, I'm Russian)).
Refer to the previous imgur link.
But it still tells you it's not some kind of no name thing, but official thing
Official≠Canon. Official just means it is approved by the registered Mark.
Crossovers like Luffy's one in Dragon Ball are official, because the one who holds the registered mark of One Piece allowed it to happen. Pretty sure you'd also find them on the credits of said crossovers. Doesn't mean they are canon to all series involved.
Tl;Dr:
- Editors have claimed not to have watched sagas of the work so they put incorrect information that couldn't fix until a later version of the book where they already watched said sagas (so, who's gonna confirm there are no other mistakes he didn't realize/couldn't fix? Why would the information given by someone who hasn't even read the work completely at the point of some books even matter?)
- Part of their sources are videos, guesses and fans' opinions, truly not a reliable source
- They fill the gaps of information with their own headcanon, admitted several times. Meaning the word is not entirely reliable (something they even say: "we don't claim to be entirely accurate")
- Fail to even state easily-verifiable information like Frieza's and Goku's power levels or SSJ's multiplier.
So, yeah, this is not the case of any databook you could think of (because it isn't a databook, just a d&d-esque book to explain in a general manner how things work so the one reading can take the position of GM)
Edit:
I just found this. Point proven by Editors' word