Great article! Just a note about these three nutrients you mentioned from a long-time nutrition-science nerd:
1. B12 is a supplement everyone should be taking, due to soil depletion (globally) even grazing animals need supplements these days.
2. Don't forget to supplement vitamin D! While most doctors believe that a little time every day in the sun is sufficient, a few studies from over a decade ago demonstrated that the vast majority of people are vitamin D insufficient regardless of diet or outdoor activities.
3. Nobody who isn't literally starving develops protein deficiency. The important thing when it comes to macronutrients is getting the right proportions of proteins to fats to carbs to fibre. Most whole plant foods have good proportions, whereas animal products tend to have far more proteins than other nutrients which isn't good for us long-term.
4. Iron is a weird one, the science isn't 100% clear but it looks like we're only able to measure what's in our irons stores, when what really matters is our blood levels. If I recall correctly it might actually be dangerous to take iron supplements when you don't need them.