Reading on this a bit more, it looks like I was off on B12 specifically. Vegetarians can get this from eggs and milk, but full vegans need to either eat plant-based foods that are fortified with B12, or directly take a B12 supplement.

So my first sentence should actually be, "All essential nutrients humans need can be provided by a plant-based diet." That is accurate because it includes fortified plant-based foods, plant-based direct suppliments, and vegetarians.

the distinction between food and supplements is purely regulatory and semantic. at what point does something become a food or a supplement? if i lack vitamin c and i eat an orange, have i supplemented with vitamin c? b12 supplements are made through microbial fermentation, like alcohol or vinegar or lactic acid. if i need iron and i take a pill, i've supplemented with iron, but if need sodium and i eat salt, have i supplemented? starch and sugar are simple chemicals extracted from whole foods, yet they are still considered foods. my point is that there is no true objective distinction between food and supplements, it's just a vague label like "natural/unnatural"