One of the comments on yesterday's blog post pointed out that most/all Nancy Drew ghostwriters are under contract to never reveal their identities. I find that to be rather interesting, because other ghostwritten series--Animorphs, The Baby-Sitters Club--list the real author's name on the dedication page. They don't keep their ghostwriters' identities a secret. Nancy Drew does.
We do know some Nancy Drew ghostwriters, but I'm not sure how they were revealed. With the modern (i.e. in the past ten years) books, two ghostwriters are listed on Wikipedia. That's how I found out about them. No source is listed, but the information is accurate. At least, the one author is accurate, and confirmed their identity. I haven't tried to contact the other author.
The only other ghostwriter we know of from the modern era is George Edward Stanley, and we know about his ghostwritten work, because he died and donated all his stuff to a university. I would love to go there someday and read his various manuscripts for the book that became the Trail of the Twister videogame.
With the previous era of Nancy Drew books (80's and 90's), most of the ghostwriters we know about are authors who decided to reveal themselves, because it's been 20 years at this point, and it doesn't matter anymore. So they posted about it, on their websites or wherever. About 5-6 ghostwriters have been revealed this way.
We know every single ghostwriter before then, because that information was revealed when Nancy Drew got new owners in the 1980's. All that information is public knowledge, available on Wikipedia. I would imagine most of them are deceased at this point.