People sometimes refer to books like this, or the Heinz Handbook of nutrition, and come up with what seems or may seem lige 'vaguely documented' B12 levels in plants. Here's something I found today, which I believe is from one of these sources, slightly rewritten:

Green Beans 0-0.2
Beets 0-0.1
Bread, wholewheat 0.2-0.4
Carrots 0-0.1
Oats 0.3
Peas 0.0-1.0
soybean meal 0.2
black beans 0.1- 1.0
red beans 0.1 - 1.0

(also lentils, wax beans, chick beans and some other kind of beans).

Being a sceptic, I don't trust all the results I see, as explained in many other posts. OTOH, these aren't just made up from nothing, and don't even come from vegan, over-enthusiastic evangelists who want to prove that eating vegan is "natural" (as if we need that argument - even clothes or houses occur "naturally" on our planet!).

But, as an experiment: the average of all the above mentioned values is circa 0.2 mcg/100g. I have already mentioned that people eg see that some B12 is found eg in mushrooms, and say that one would have to eat a lot of mushrooms to get enough B12. But then someone else reads that there's some B12 in organic spinach, followed up ny saying that one would have to eat a lot of spinach to get enough B12 fro spinach. And so on. And then there's the thing with active B12 vs inactive analogues. We usually don't eat fresh food - and nowadays most people don't eat only organic food (they did a few hundred years ago).

So, here's another little mathematical experiment: how much food and water would one need to drink if all food and water contained 0.2 mcg B12/100g, based on the rather common RDA of 2.4 mcg? The answer is 1.2 kg. Most people consume a lot more food and drink per day than that, but then again - not all food contain even micro-amounts of B12; some doesn't contain B12 at all, and some food may contain B12 in so small amounts that they aren't measured properly eg because food is heated when B12 is measured, and heating destroys B12. Plus most of us do heat food anyway, and the raw fooders who claim that they are doing fine without taking B12 may to some degree me right due to the fact that the micro-amounts of B12 they get isn't destroyed by heating. I still think it's a good idea to take B12, to feel more safe (and I'm not a raw fooder anyway)... but IMO it's a good idea not to ignore findings of very small amounts of B12 in plants based food, at least when it comes to the "Can a vegan be good for us/natural/recommended if it contains no or little B12?" discussions. Humans rely on 'culture' for everything, and unlike almost other mammals, we (vegans and meat eaters) wouldn't survive long without man made ("unnatural") inventions; that is: actions that are a part of our culture and not our nature.