Yes! Deficiencies could occur from multiple sources as well.

I found out from my doctor I was deficient in vitamin D and calcium probably due to diet I'm allergic to milk. So I started taking vitamin D and calcium supplements.

Later I found out from my personal genome study, that my body doesn't process vitamin B correctly, so I need much larger doses than the average person.

I think once people begin to get personalized genome information, a lot of misinformation surrounding diet,vitamins, and nutrients will be cleaned up.