Once again, it's Tarantino. I'm sure Mandingo is more a homage to the movie Mandingo (which I haven't seen) than historical times.
I dunno. Here's Tarantino's quote from an interview.... IMO, this sounds like he's claiming it really happened historically.
I wouldn't say that Inglorious Basterds was exaggerated, in the sense that even though it was far from historically accurate, the Nazis were guilty of crimes far more insane and grotesque than whatever Tarantino depicted in that movie.
Saw Django on Monday night, just released in the UK. Outstanding, up there with his best I would say. 9/10