Why are vitamins named the way they are? (A, B, C, D, E and so on)

When they were naming vitamins they must have thought there were going to be way more vitamins than there ended up being. OK let's name these: Vitamin A, Vitamin B... Ok, man, slow down, we've got a lot to cover here. B2, B3, B4, B5, B6, B12. Then they got to E and they were like 'We're pretty much done. We've got all those damn B's. This is embarrassing. Let's just skip to K and get the hell out of here.