The Prince of vitamins... Sadly, it's in oranges, not raspberries

I'm a fairly health-conscious person who eats a lot of vegetables. I'm sure I get plenty of vitamin A since I eat more than a pound of carrots in an average week. I get lots of C from peppers, and the slightly-obscure K from leafy greens. So I was floored to see this in "Sunkist Orange Recipes for Year-Round Freshness!" (1940, and yes, the California Fruit Growers Exchange thought "freshness" needed to be underlined):

No, it wasn't the vitamin C, A, or B that surprised me. It was vitamin G, which apparently must "be replenished daily."

I had never heard of vitamin G. Did the California Fruit Growers simply make it up so they could sell more oranges, as there was no other source of this elusive vitamin? Was it some kind of joke or slang? Then I checked Wikipedia and found out that it's the Prince of the vitamin world. Vitamin B-2 "is the vitamin formerly known as G."

That's cool to know, but "Orange Beret" doesn't have quite the same ring to it.