Common foraging rhetoric is that you need two independent sources asserting that a wild food is edible. Ones that cite neither each other or the same chain of citations. And preferably a human who says, "I've been eating these for years and no problems." or scientists who did recent blood work to make sure you aren't destroying your organs by eating [1].

In a world with fake books, it would be quite easy for two books to contain the same misinformation or mis-identification (how many times have I found the wrong plant in a google image search? More times than I care to count). Two fake books putting the wrong mushroom picture next to a mushroom because they were contiguous on some other page and you have dead people.

[1] In the ten years since I started working with indigenous plants, wild ginger (asarum caudatum), has gone from quasi-edible to medicinal to don't eat. More studies show subtler wear and tear on the organs (wikipedia lists it as carcinogenic!) and it is recommended now that you don't eat them at all, even for medicinal purposes. I'm not sure I own a foraging or native species book younger than 5 years, and many are older.