CC September

[Ambiguity]

I heard Dave rarely uses reference though.

To be fair, he did actually hear this:
https://www.youtube.com/watch?v=b4BtCbrv....be&t=9380
"I don't really reference anything, I try to keep it all from my imagination" - Dave Rapoza, Level Up! Session 43

"I don't like to use reference that much for these images because I like to go and try and find like a more cartoony, maybe like in between feel. Just what's in my head, I don't want to be bound by the reference image. So, I'll keep working until I hit a wall and if I absolutely need to reference something for whatever reason, like maybe like gross teeth or something, then I will....but I want to get as much as myself in this as possible." - Dave Rapoza, Bog Witch Tutorial Part 2 

Keywords in those quotes are "don't really" and "that much", he didn't say he never references, and neither did genos. Incidentally, I've also heard Wesley Burt and Karla Ortiz express similar sentiments to the latter quote(actually she said she learned it from the Massive Black guys). All of them are advocates for studying from life, photos, and master works however, so in a sense you're always at the very least mental referencing(although I consider this to be different from what artists like Rockwell were doing).