Most of the modern Nancy Drew authors are unknown ghostwriters. One of the few we know about is George Edward Stanley.
The reason we know about him is because, well, he's dead. The University of Southern Missisippi has a copy of most of his various manuscripts.
I wish I knew about him, before I did my review for The Mystery in Tornado Alley. It turns out that the book does NOT take place in a fictional university in Oklahoma; it takes place in the university where George Stanley worked as a professor. (Stanley always mentions Oklahoma somewhere in his books, as an Easter egg. This makes me suspect he wrote the other "Nancy Drew Goes to Oklahoma and Meets University Professors" book.)
Also, I'm surprised that the Tornado Alley book went through four drafts, considering how awful the final book was. I wouldn't mind going to Mississippi and reading all four drafts of the book, just as a matter of curiosity. That's probably never going to happen, but I'm sure it would be interesting!