He openly said he wish he'd done more research, and then said he didn't consult anyone at Obsidian, or her chief writers about her, and didn't Play KOTOR 2 enough to truly understand the character in a way you don't get from sourcebooks.
On the basis of what Karpyshyn wrote in the novel, it seems that he didn't start as a blank slate on her either. The author got most things about her right somehow.
Also, such level of neglect is very common among the authors of Star Wars mythos, specially when they write about characters that are not their own creations. Only Luke have been put on pedestal as per my knowledge but some authors have still depicted Luke as a man with limits or refused to hype him.