[Langus]

I think there's a reason that low level shinigami who don't work under her have been shown to be terrified of her in the past, or at the very least didn't want to cross her. This suggests to me that there is, like sayde said, an underlying knowledge or rumour of her past. She's part of SS legend in the same way that Yamaji was and Kenpachi is.

But rumours are only rumours. Chiaki chan has a point too - only the higher ups or those who've been around SS long enough would know the true extent of Unohana's past. I would argue that those working under her, even her VC, don't know the whole truth.