You think early humans ate raw livers for vitamin C? Sounds unlikely. We are omnivores, and except for rare exceptions (I.e. on the Northpole) plant material is more abundant than animals.
Before the age of human agriculture we were endurance hunters. Don't believe me? Go survive off of random unidentified plants for a while. (Don't actually, you'll be dead in a month tops).
That's discounting the cultural plant knowledge that those hunter gatherers had.
100k years of 'Don't eat that, it kill Grog remember?' can lead up to a pretty extensive safe list of wild plants as well as a bunch of useful healing herbs.
We've long since forgotten most of it, having not needed it since agriculture.
Livers were prized parts of the animal for hunts, we knew the value of organ meat before.
Just now everyone is like 'ick, organ meat'...
That said, I don't know if I trust modern livers, they are the toxin dump of the body and while I'd happily eat liver before the industrial revolution, I'm not sure its safe to eat now considering how we treat our farmlands.
Most people don't bother looking into it other than what they read on blogs or see on youtube. There's a LOT of nutritional misinfo going around. Thats what happens when social media values reach and clout over accuracy and meaning.